My Headlights Stay Up After Adding Headlight Relays

[Ronnie]

I feel my previous post has been successful in it's intended purpose of raising discussion about how to best put solution to the problem in the hands of all Reatta owners. Taking the load off a scarce part, the headlight switch, and transferring that load to a relay that is readily available at an auto parts store makes good sense regardless of how long the original switch lasted.

I'm happy to hear that Mc_Reatta is considering producing a kit. I hope it works out. In the meantime it would be a good ending for this thread to post a final wiring diagram and summary of how it should be used for future readers.

[juddev]

I was just doing a little reading and came across this diagram using the neg wire to trigger the relay, I wonder if that might produce the proper result.

Circuit 3 shows turning the relay on/off with the ground wire instead of +12V. This might be an easier way to wire a relay depending on the situation.

[drtidmore]

Great work guys!

David T: I think some of your calculations in post #60 are unnecessarily pessimized.

The HDM will not be "floating" as it will remained tied to ground through the relay coil. Granted the relay coil is 87-90 ohms as compared to the 2-3 ohms of a headlight filament, but still a solid path to ground. In my situation with HID low beams, there is NO low beam filament to ground through. I could put a 5 ohm power resistor between 87a and ground which would be similar to an actual beam filament but I am not convinced of the necessity.

You may have misunderstood the voltage points that I chose for my calculations. 9 volts is the PULL IN voltage for these heavy duty automotive relays. It has nothing to do with anything I measured on my Reatta. 4volts is the drop out voltage. I was pointing out that adding a series resistor to the relay coil to get it to drop out under the 5.2v HDM sense voltage, you run into ohms law in that by the time you find an added resistance to ensure that the relay coil is below 4 volts, that SAME resistor is likely to ALSO ensure that the relay coil never sees 9volts (ie too much voltage drop across the added resistor).

As for the alternator I agree that the one on the Reatta is a like a rock (mine is 25 yrs old and never been off the engine), but you should use conservative assumptions when calculating whether you might or might not be able to have headlights. Everyone makes their own decisions as to risk acceptability, but as an EE, I will stick to what I posted.

David T

Edited September 2, 2013 by drtidmore (see edit history)

[2seater]

I know this thread had some detours due to not immediately understanding the suggested configuration and a bad selection of relays, but to ask why you would do this escapes me? In any case, I need to relate an additional happening that was not done during testing, primarily because the brake pump was apart and I couldn't fire up the ignition:

When I substituted the OE Hella relays from the relay center, the headlights operated as predicted, as previously reported. I then returned the Hellas to their normal duty and installed one Bosch and one PEI relay until I could get a good matched set with mounting tab. The headlights worked exactly as with the Hellas, all normal, or so I thought. I completed the brake work and started the car to go for a drive. For whatever reason (it was mid-afternoon), I tried the headlights before leaving the garage. They turned on and opened just fine, but would not close or go out. The marker and tailights do turn off, so the H/L switch is functioning. I switched the lights to hi beam and tried turning them off and they did, as well as retracting as normal. I turned off the engine and just turned the ignition to run, and then tried the headlights, which again worked perfectly. I repeated the engine running test, and it did the same thing, if in low beam (default) position, the headlights lock open and on. I went back to the Hella relays from the relay center and they worked perfectly no matter the engine on or off. For some reason, one or both of the two other brand relays is either defective (brand new) or something doesn't like the higher voltage of the alternator charging the system. I did have a battery charger on the battery during some of the original testing, so I don't understand what is going on? I tried looking up the various relays online, to see if I could see differences in the coil assembly. I did not find much but the closest part numeber I could find for the Hellas indicated 85 ohm coil and no mention of diodes. The PEI stated a 90ohm coil, but not much else. The Bosch was no soap at all. I will list the part numbers below, but apparently this setup is sensitive to a specific style or type of relay coil assembly. Perhaps the electrical brain trust can divine something from this information so a more specific, commonly available relay can be included in the finished product.

Hella 960388-02 (O.E. relays)

PEI AR-5

Bosch 0332204125

[2seater]

I posted too soon. Since it is now dark, I went for a short drive, just to see how things look with newfound brightness. There is no doubt there is a large improvement. Since they are E-code lights, the road signs light up way far ahead. They did so somewhat before, but they can be read at extended distance, not just glowing. I digress from the actual message. After only a ten minute drive, I tried to turn the lights off and the same failure of function occured. On low beam, the lights are locked in the on position, turning to hi beam, they will turn off and close. I repeated the previous test, with ignition on and engine off, and they work fine. Start the car, turn the headlights on, and they are locked there.

Immediate followup to what was just said, while this post was still open, I went back out to test another combination, headlights locked on and then kill the ignition. I did that earlier when they first stuck, and it started ticking, so I wanted to confirm, but now they work perfectly, six times in a row, engine running. I am completely lost.

[Guest Mc_Reatta]

Think you need to drive your Reatta to your local Witch Doctor and have them drive the evil gremlins out. :eek:

The different coils between your relays will make a difference in how they perform in this application.

Did you ever try swapping out the hi/lo beam relay to see if that does anything?

Long shot, but worn dirty contacts on the lo side could be an issue.

I'm beginning to wonder if the retained 5 volts on the signal wire isn't from the BCM not the HDM. Would have to take something apart to test though. Switching the beam relay is done by the BCM. HDM doesn't care what beam you are in, just are the lights turned on or off.

I take it when the lights stay up and on after switched off, waiting for a time made no difference.

[2seater]

Well, the Hellas that are operating the lights are used, they are the O.E. ones for horn and a/c. In their original location, they do not use the 87a terminal, so who knows the actual condition? I did look at the signal to and from the BCM at the original hi-lo relay in the console and it all looked correct. The wire feeding #86 on the hi low terminal is always hot and the BCM switches the ground on #85 to operate. Voltmeter showed voltage on both 85 & 86 in low beam and 85 goes to almost zero when switched to hi as the BCM makes ground.

I did not wait more than 30 seconds or so when the lights locked on. What I was trying to confirm when I found everything working properly again: I had previously turned the car off when they first locked on, and the lights started to make a sort of ticking sound that didn't seem to come from the relays, more from the headlight motors. After maybe 15 seconds, the lights shut off, but I think they stayed open. I only did that the one time and wasn't recording what was going because I was so surprised.

I will go to NAPA or a better parts store to see what I can find for quality relays. The only things I found close to my house are generic junk (IMHO) relays at the FLAPS. That has been getting more disappointing as I may as well order from JC Whitney relative to the quality. I will install three new relays as soon as I can find something, hopefully monday.

[drtidmore]

I'm beginning to wonder if the retained 5 volts on the signal wire isn't from the BCM not the HDM.

I have wondered the same, but our collective empirical testing seems to point to the HDM as the more likely source, even though the BCM is the controller for the high/low beam functionality. Since the HDM and BCM share the wiring to the headlights, as you pointed out, it would require pulling the HDM out of the mix and doing the measurements. Regardless, since at the end of the day they both still have to be connected it really won't change the solution.

2seater, you are chasing too many variables. Getting a GOOD set of identical relays with NO diodes in the coil circuit should be the first step to bringing some sanity to your efforts. Given that you mentioned only two relays, I assume that you are doing a common enable relay along with a common high/low beam relay driving BOTH headlights, correct? It would be instructive to know exactly WHERE (physical location) in the wiring harness that you connected the relays, just so that we tie down all the variables. I am planning separate relays for low/high for each headlight (4 relays total) with no common enable so that I can have the HID low beam remain powered when I switch to the Halogen high beam (simple diode will do the trick for that). I understand that it is a bit of a mixed bag, more relays, more points of failure, but as long as these relays only deliver relatively low current in relation to their rated current, they are extremely reliable AND they are readily available. Also, having 4 relays (2 per headlight) allows me to just plug into the factory headlight connector with NO upstream wiring mods. Each headlight harness will have a single 10 gauge fused wire directly to the battery. As soon as the weather here in Dallas decides to drop out of the 105 range, I will get out and get this all installed so that I can do further testing to ensure that what you encountered is specific to something in your setup/car rather than generic. You may well have stumbled onto yet another unknown behavior, so I am anxious to verify on my Reatta.

David T

Edited September 2, 2013 by drtidmore (see edit history)

[2seater]

David T., I am using discrete high and low beam relays as described by the original post. One relay for the low beam and one for the high beam.

I did replace the three relays this a.m., the two headlight and the original hi-lo relay in the console. I wanted all identical relays, but I needed one with a tab to hang the pair under the hood. The two without the tab show only a switch symbol for 85-86 terminals. The one with the tab shows the switch but also a small rectangular box connected across the switch symbol (resistor?). I could not find an exact match which included the tab. This is the exact same symbolism depicted on the O.E. Hella relays. I measured the coil resistance and the two without tab are 85ohm and 87ohm, with tab is 75ohm. I measured the three removed Hella relays and all are right around the 75ohm reading. I also checked across the #30 and 87a terminals and all used Hella relays measured less than 1.5 ohm. For reference, with the alligator clips in place on the VOM probes, I see almost 1ohm resistance in he probes themselves. I didn't check the new ones. The one anomaly, and possibly the source of the erratic operation with the engine running, is the O.E. hi-lo relay from the console shows apparent heat damage on both the 87 and 87a terminals. I did not notice it before when in the garage and under the dash. I had previously had the rear cover on the relay center in the console removed and actually pulled a couple of the terminals out and no heat damage was apparent. The heat looks to be from the inside of the relay as is darkest right where it meets the case. I'll open it up and see what it looks like inside. Not preferred, but the relay with 75ohm coil is on the low beam and the 85ohm on the high beam. Engine running, I cycled the headlights at least a dozen times with various "on" times and they function perfectly. Only time will tell I guess.

Just one other note, or perhaps rant. I went to four different FLAPS; Autozone, Advance, NAPA and finally Carquest (actually sent there by the NAPA guy). Two places have the exact same junk, NAPA couldn't seem to find anything without a reference number or car model, but the Carquest guy took the time to look through the box of relays with me to find what I ended up with. If I had the luxury of time, I could have ordered exactly what I wanted online.

Thanks for your patience and assistance.

[Guest Mc_Reatta]

Aha 2seater! Glad you finally took a good look at that hi/lo beam relay. The damage you see (and what is hidden inside) is what's going on inside us 80s owners headlight switches too. You 90s owners are getting that kind of damage even with the added headlight relay.

Sounds like Carquest has risen to the top of your FLAPs list.

So with the 3 new relays everything is copacetic?

DavidT, let me buy some stock in the relay mfg company before you put your harness together. Don't know why you want to go to that extent unless you want to be able to get your headlights to wink when a pretty girl goes by.

I had thought about adding that combo hi/lo mode as well, but after discussing with wws944 decided against it with either standard sealed beams or H4s that house both filaments in the same package. Don't think HIDs or LEDs would care, but they aren't in my sights at this time.

[2seater]

I used to have a day job, and the headlights weren't used much, as I really dislike the look, so I suspect the switch didn't get the same abuse it does now. I have had 80/100 Hella lights for a long time, better than ten years, so I was able to prolong the original switch life by simply not using them. A night owl job and I lost two switches in six months. Coincidence, maybe? I have tried the hi-lo combo in a single bulb, Ranger pickup, and it definitely gives a nice view. The Silverstars have survived this abuse several times, but I'm sure the life has been reduced. On the Ranger, pulling the dimmer stalk will light both filaments just before going through the detent and can be held there. On very dark winter nights, in rural areas with extremely high deer populations, I felt the potential cost worthwhile. It has the side benefit of keeping the fog lights engaged as well, which were converted to Cibie driving lights. An old Saturn could be operated the same way but had four bulbs. The computer operated lights on the Reatta preclude doing anything like that.

[drtidmore]

A night owl job and I lost two switches in six months. Coincidence, maybe? ... Hi/Low combo..the computer operated lights on the Reatta preclude doing anything like that.

2Seater, remember that the factory switch AND wiring were designed for 35W low/50W High filaments and you upped them to 80/100. It is little wonder that you burned through two headlight switches in six months. The switches may WELL have saved your factory wiring. That factory hi/low relay showing heat damage is the result of pulling TOO much current through the relay. Good thing that you have removed the current carrying to the new harness and away from ALL the factory stuff.

As for the HI/LO combo on the Reatta, with the addition of separate low beam and high beam relays, this is SUPER easy. What you need to do is install a diode such as a 1N4001 between the positive connections on BOTH relays coils with the anode to the High beam side, the cathode to low beam. With this setup, when you engage the low beam, the diode BLOCKS the voltage feeding up to the high beam. On high beam, the diode ALLOWS the voltage that activated the high beam relay to ALSO activate the low beam relay. As for the impact of backfeeding 12V from the High Beam relay coil to the low beam relay coil and by association, the factory wiring all the way BACK to the hi/low selection relay, remember that the factory Hi/Low selection relay is a SPDT relay, so when high beams are selected, the relay contact for low beam is TOTALLY disconnected from EVERYTHING, so there is no harm in back feeding. The only thing that needs to be ensured is that the wiring from the battery feed to the new low beam and high beam relays and the ground wiring on the actual headlights is UP to the job of carrying the necessary combined current that BOTH beams will pull (and YES! you do HAVE to ensure that the ground wiring is adequate as much as the +12V feed).

Now as to whether it is a GOOD idea with your particular headlights is a WHOLE other subject (ie heat). I contacted the manufacturer of my HID housings and enquired as to the heat issue (being glass enclosures I already suspected the enclosure would be fine). He added that the HID and Halogen bulbs chosen and their placement was indeed designed for simultaneous HI/LO beam activation. As my new HID low beams are 35W / 50W Halogen high beam, even if I did NOTHING, I am NOT stressing the factory wiring or the headlight switch any more than the original Halogen bulb. Switching from the really excellent HID low beams to the Halogen high beams is like stepping back to 1989 (ie the high beams are horrible compared to the HID low beams). Regardless, I am moving ALL the current away from the factory circuits ASAP as I want to protect my almost virgin headlight switch that I installed recently (my 25 yr old switch worked, but the off button was wonky about cancelling park lights)

David T

[2seater]

David T., I always knew in the back of my mind that the hi wattage headlights would be an issue, although I didn't suspect the headlight switch as the weak link at the time. As I said way earlier, I knew better, but out of sight, out of mind.

I don't have time to go into detail at the moment, but you had asked if there was a previous issue with the lights and the answer is; maybe? I have been thinking about that and being at work sparked a memory. In any case, as Yogi would say, it's Dej'a Vue all over again. The headlights locked open at both ends of my 10-12 minute commute to work and back last night. Switch to high beam and everything turns off. I'm thinking headlight module. The BCM only makes a ground to trip the hi-lo switch. Can't see where stray power would come from.

[DAVES89]

Hal I have 3 on the shelf. Call me if you need one...

[Guest Kingsley]

At this point, I am moved to say "thanks" to all of the folks who have contributed to this this thread. I am a bit of a freak when it comes to headlight operation but from a different aspect, much simpler that than being discussed here.

The expertise when has been displayed is of the highest caliber and is quite a source of comfort to all users of this Forum.

Kingsley

[wws944]

Minor point: The original Guide H6054s only have a 35w low beam. But they have a 65 watt high beam. So in theory, the factory wiring and switches should have been designed for 2*65w=130w - which would be about a 9.5 amp draw when the engine is running. It is strange to me that they would have used a 20 amp fuse in the circuit. Seems to me that 15 amps would have been a better value, to avoid exactly the problems that 2seater encountered.

It is also interesting to me the timing of GMs mid-1990 relay mod. They had already gone through four model years of switches in the 86-89 Riv, and of course the 88-89 Reatta. Then half way into the model year of the redesigned 1990 switches, they quietly added the relay - both in the Riv and Reatta. Were they starting to see lots of warranty problems in the 86-89 switches? Seems like the 1990 relay mod was made before they would have seen a lot of 1990 warranty problems as motivation for it.

Edited September 3, 2013 by wws944 (see edit history)

[Guest Mc_Reatta]

Kingsley: didn't you make up a breadboard of the door motor circuits a while back to test your replacement parts?

That might prove useful as I think you incorporated a HDM but probably didn't include a BCM. That would be an easy way to find out where this nagging 5 volts is coming from when headlights are switched off.

[Guest Kingsley]

Kingsley: didn't you make up a breadboard of the door motor circuits a while back to test your replacement parts?

That might prove useful as I think you incorporated a HDM but probably didn't include a BCM. That would be an easy way to find out where this nagging 5 volts is coming from when headlights are switched off.

McReatta - my test stand was "full blown" and did incorporate the BCM. Unfortunately, it is currently dismantled and in storage. Having said that, it indeed will live again in the near future and I will be glad to do any diagnosis work that would be of help.

That test board was extremely helpful in my pursuits.

Kingsley

Edited September 3, 2013 by Kingsley
Modify Text (see edit history)

[2seater]

Oh man, I just returned to this thread again and I see my post from the this morning is missing. I will try to summarize as I am just too tired to hunt and peck type it again. The problem with the lights staying on is back, and will do it almost anytime the lights are on for more than a minute of two, at least after everything is warm. It is actually somewhat predictable. Leave them on with engine running, wait a couple of minutes and turn off. Won't go out or close, turn the switch back on, switch to hi beam and then turn off, everything works. Tried something I mentioned before, headlights stuck on, turn engine off. A sort of light knocking sound is heard from under the hood, very regular. It lasts maybe ten seconds and the lights go out but stay up. It doesn't last long enough to really pinpoint the sound but seems to from the area of the transaxle or where the air filter would normally be. Really hard to tell. The relays are in that area, sort of. They are mounted on the outside of the relay center, but it definitely isn't the click of a relay. A much heavier sound although not loud.

I drove my car to work for the first time in a month last night and this triggered a memory of some other odd behavior. I will try to give a quick overview of the two possible clues to previous issues with the headlights. Several months ago, shortly after I installed the replacemnt H/L switch, when I arrived at work, I noticed the headlights turned off but did not retract. I chalked this up to shutting off the ignition at the same time as turning off the lights. I didn't know much about how this system works at the time so I thought it a coincidence. Turning the lights back on and then off again cured that issue. Never happened again.

In early Aug. my replacement switch was getting crunchy feeling when operated. I was a little concerned but it seemed to work fine. One night on the way to work, the headlights suggested warning came on and I noticed the pilot light was out in the switch, although the headlights were on at the time. The lights did turn off normally enough. About two hours later, I was informed my lights were on in the parking lot. I went out to turn them off and it took several tries for them to go off and close. A couple of hours later and the same thing happened. I don't remember if I closed the doors manually or with the switch, but I determined it would be a good idea to at least pull the plugs at the bulbs to save the battery. As I removed the second plug, the lights popped right up, narrowly avoiding a nasty finger pinch. I ran them back down manually and went inside. It was about two hours later when leaving work, there it was again, with the lights up. It did it a couple more times at home in the driveway and I finally pulled the headlight switch, which was now stuck so the button cannot be depressed. I used the car a couple of days for daytime errands and the self-activation did not return. The rest has been detailed in this lengthy thread.

[drtidmore]

So basically, you had gremlins well before adding relays to directly power the headlights and that behavior is intermittent but recurring, or so it would seem. Since you have seen similar behavior with just the factory circuits, it would probably be a good idea to get back to factory configuration and solve the initial issue. I think I would return to factory spec beams at least until you can sort this all out. At the moment, there are too many variables in play.

David T.

[Guest Mc_Reatta]

2seater, didn't realize until one of your recent posts that you have been running 80/100 watt bulbs for some time. The past problems you recalled sound like they are all related to headlight switch failure most likely from welding those contacts with the high current draw.

If I were you I would try using a pull down resistor on the ground leg of the new lo beam headlight relay. I suggest a 33 ohm 1/2 watt one out of a 5 pack from Radio Shack for $1.50.

As long as your alternator supplies 13 volts or more, this should put 9 volts across the relay which should turn it on fine. When shut off, it will drop that retained 5 volts down to 3.5 volts across the relay which should cause it to drop out reliably. Once it drops out, that voltage will be pulled to ground thru the connection on pin 87a and the headlight filaments and doors will close and lights turned off.

Without the alternator running, the battery 12.6 volts may not be enough to get that relay coil to engage. But guess what. The doors will come up as that is plenty for the HDM to raise the lights, and since that voltage is also directed to the lo beams thru the connection at pin 87a, the lights will come on, but the power will be coming thru the headlight switch and not direct from the battery to them via the new relay. One you start the car and the alternator kicks in, the relay should engage and switch the headlight power over to the battery. You might see a quick flicker in the lights as the power is switching over as the relay engages. If there is a problem with the coil engaging with a 33 ohm resistor, swap it out with a 22 ohm one. That should get it to engage easier, but will make it more likely to remain engaged after lights are switched off.

Even so, worst case without the engine running or a bad alternator, you have the same situation as you have been using for years. And how often do you really turn your headlights on without running the engine except for a quick check, or drive around with a bad alternator?

[2seater]

I really cannot go back to the complete factory setup, since I don't have the defectiive switch, the headlights got new sockets connected to the new wiring. The old headlight sockets have been removed as they were partially melted and no longer serviceable. I believe I will replace the HDM, if for no other reason, I will then have a spare if it does not change the behavior. I did notice a small note on the lower right of the FSM on the pages for the HDM wiring. It mentions a six second time out on the HDM if there is a defect in the headlight motor or crank assembly. That sounds oddly like the time the lights remain on after the lights retract? It also sounds sort of like that odd knocking sound I can cause under certain conditions. I am only guessing, but if there are two sets of moveable contacts inside the HDM, perhaps that is what I hear but muffled by the enclosure? I need to have a helper so I can be in the right area if I can cause that sound again. If indeed the HDM is the cause, and it is not defective, the workaround sounds like a resistor to get the control voltage down? I would guess the other option is to relocate the connection for the yellow HDM control wires to the output of the headlight relays, yes? I know the thrust of what we have been talking about is to not modify the standard wiring, but I am more than willing to give that a try if you think it would work? The splice for the twin wires to the HDM is very accessible and close to my relay location.

[Guest Mc_Reatta]

Well, I couldn't be more corn fused if I was from Iowa! :confused:

I read the notes in the 90 & 91 FSMs, reread the one in the 89 FSM, and can't keep from scratching my head.

They depict a much different operating design from each other. Then I rechecked the parts list to confirm the same part number was used for all 4 years which it is.

So we have 2 parts that are interchangeable, with the same part number, but operate differently. And to add insult to injury, the symptoms that DavidT and 2seater report are bass-ackwards from what I would expect from the year of their cars.

Enough whining though, need to address the situation and come up with a plug and play solution that will work in any car.

So I will stick with my recommendation of using a 33 ohm pull down resistor on the relay's coil ground wire. Depending on the results may have to go up or down a step to get the desired result. If that won't achieve a good result, will have to go back to the drawing board and come up with an isolating circuit that will.

[wws944]

Well, I couldn't be more corn fused if I was from Iowa! :confused:

I read the notes in the 90 & 91 FSMs, reread the one in the 89 FSM, and can't keep from scratching my head.

They depict a much different operating design from each other. Then I rechecked the parts list to confirm the same part number was used for all 4 years which it is...

Way back in post #31, I mentioned this Fiero thread:

Pennock's Fiero Forum - Installing Gen 2 Firebird Headlight motors into Fiero (by masospaghetti)

If you look towards the bottom of it, in MSG #33, the poster claims the '90-'91 Reatta module has a different part number than the '89. (He doesn't mention the '88 Reatta.) So it seems like there was a running change between the years.

[2seater]

Just to add a little more information: I uncovered the splice where the yellow wire to the HDM splits, near the underhood relay center. I clipped an old panel voltmeter on the splice and I find approx. (5) volts when the lights are switched off with the engine NOT running, and the lights close, but stay illuminated for 5-7 seconds as they have been doing. I then checked with the engine running and I see 6.5 volts when the ligts are switched off, and they are locked on and open. I then shut the engine off, and after a very short time, just a few seconds, the voltage disappeared and the lights went out but stayed open. I did not not any knocking/tapping sound I had reported before. This test was done after the car had sat in place for more than 24 hrs and the headlight test was done immediately so everything was cold. I am going to read through the Fiero experience and appreciate the link but didn't read it the first time through.

I'm certainly no expert but at first blush it appears to be different than ours. Maybe just the way it is displayed and they are doing some motor changing as well. I will try a resistor and probably also relocation of the yellow HDM wires. I know you want a kit to plug and play, and I would guess an adapter harness that goes between the HDM and the connector could be part of the harness? That sort of thing is done in many forms, like plug in trailer wiring for example? The 87a connection wouldn't be needed through the relay either, the likely source of the problem IMHO. Also just an uneducated guess, but wouldn't the proper resistor be dependant on the resistance of the coil? I measured a 15 ohm diffence between one coil and another, or between 75 and 90 ohm depending on the brand or style.

Edited September 5, 2013 by 2seater (see edit history)

[drtidmore]

There is a potential solution to this problem. In reviewing the '89 FSM, I have determined that by adding one additional relay to isolate the HDM "Headlights On" input from the actual Headlight circuits, the problem of the HDM holding the added bypass power relays vanishes. As the HDM "Headlight Doors Open" input is factory blocked from backfeeding by the "Headlight Door Diode" (at least on the '89), there is no need to isolate it. It looks like we can just mod the factory wiring AT the HDM (under relay center in engine compartment) and avoid messing with the wiring behind the instrument panel. The HDM "Headlight Doors Open" input is the yellow/black wire on the HDM (to be left AS IS) and the HDM "Headlights On" input is a plain yellow one (again per the '89 FSM). Cutting the yellow wire near the HDM and inserting the additional relay would be a fairly benign wiring mod and one fairly easy to access and accomplish. According to the '89 FSM, S255 behind the left side of the instrument panel is where the wire from the headlight switch, wire to the "Headlight Door Diode", wire to the HDM and wire to the headlight high/low relay are spliced, so cutting the wire AT the HDM should have NO impact on anything OTHER than the HDM "Headlight On" input.

The added HDM relay coil would connect to ground and the cut HDM yellow wire FROM the headlight switch (ie NOT the yellow wire leading into the HDM). The cut yellow wire leading into the HDM module would be connected to relay connection 30 (the wiper). The normally open contact (87a) would be tied to a fused +12 source. The normally closed contact (87) could be tied to ground through a 2 ohm resistor.

When the Headlight switch is moved to on, the unmolested factory wiring to the HDM "Headlight Doors Open" input would be fed 12v from the headlight switch through the factory Headlight Door Diode. The new HDM relay would be engage by the same Headlight switch 12v, connecting 12v to the HDM "Headlights On" input which along with the Headlight Doors Open input opens the doors. Once the headlight switch is moved to off, the HDM relay would disengage, the relay would ground the HDM "Headlight On" input through the normally closed contact and associated resistor tied to ground (ie simulating the headlight filament) and the doors would retract with NO backfeeding of the HDM 5 volt signal. The added headlight bypass relays would no longer be held closed by the HDM and so once the headlight switch voltage was removed, the appropriate headlight bypass relay would disengage immediately.

This should make the HDM happy as it will be seeing pretty much exactly what is saw with the factory wiring (ie before the added relays). The rest of the factory wiring should be happy as well as it is unmolested. The added power relays to the headlights will NOW drop out immediately on the headlight switch being set to OFF.

This is what I am going to do with my '89 as I really want the headlights to function independent of engine running status (ie alternator voltage) and adding a series resistor to the bypass relay may likely result in inoperative modes as I and Mc_Reatta have pointed out. I am not a fan of modding factory wiring, but this is one that I am going to do.

David T.

Edited September 5, 2013 by drtidmore (see edit history)

[Ronnie]

I know you guys are sharp as tacks but I was wondering if you guys are taking into consideration the changes in resistance as the headlight filaments heat up and cool down? Is the HDM looking at that resistance to determine when to close the doors?

[drtidmore]

I was wondering if you guys are taking into consideration the changes in resistance as the headlight filaments heat up and cool down? Is the HDM looking at that resistance to determine when to close the doors?

Ronnie,

Filaments change very little between on and off states (typically a few hundredths of an ohm). In my testing, I have already shown that the HDM is quite happy to close the headlight doors with 87-90 ohm of resistance through a relay coil (ie NO other path to ground). This showed that the HDM was NEVER intended to monitor for headlight burnout as a filament is around 2-3 ohms and two of them in parallel (ie as factory wired) is half that. The HDM simply is using the filament as a return pathway to ground for the HDM "Headlight On" input, nothing more.

The issue is NOT the doors behavior that is under discussion. I found that the doors, at least on my '89, behave properly even with a single relay coil as the return path. The problem is that the relay coil is NOT sufficiently low in resistance to pull the HDM "Headlight On" input from its internal 5 volt signal to ground like a headlight would. This is causing the added headlight power relays to remain engaged until the HDM internally powers down after 5-10 seconds leaving the headlight ON after the doors close for a few seconds. Not all that bad, but it would be better to have everything behave as originally designed.

The goal is to mimic the factory setup in all aspect if at all possible. Since the HDM does NOT distinguish that a single headlight beam is out, it would take both beams to be out for the headlight door up symptom to appear and that is nonsensical. Moving the HDM "Headlight On" input to a relay isolated circuit as I proposed basically gives up no functionality, maintains all the important factory wiring (ie behind the dash) and ensures that the headlights and doors behave as originally designed.

As for what 2seater is experiencing, that is a whole other subject. He was experiencing similar issues BEFORE he added the headlight power bypass relays. He admits he had been running 85/100w beams for several years and due to heavier recent nighttime use, had fried two headlight switches. He admits the headlight sockets were melted and the high/low relay shows tell-tale signs of overheating as well. I am afraid that he has wiring issues in the form of either a bad connection at S255 due to heating or worse, problems in the wiring itself. We need to keep his situation separate from the broader issue of removing all the high current from the factory headlight switch and factory wiring. Hopefully, between the combined insight and suggestions of the forum, he will eventually get to the bottom of his headlight anomolies.

David T

Edited September 5, 2013 by drtidmore (see edit history)

[drtidmore]

The 87a connection wouldn't be needed through the relay either, the likely source of the problem IMHO. Also just an uneducated guess, but wouldn't the proper resistor be dependant on the resistance of the coil? I measured a 15 ohm diffence between one coil and another, or between 75 and 90 ohm depending on the brand or style.

Hal,

The proposed HDM relay needs the normally closed contact tied to a 2-3 ohm resistor to mimic what the HDM "Headlight On" input would feel through a normal halogen filament (ie headlight off). As to whether it actually requires +12V during headlights on is something of a question in my mind as I know that 12 volts to the HDM "Headlight Door Open" input, opens the doors regardless of headlight operation (I previously pulled BOTH headlights, and tested that exact scenario). At least in the '89 design, the Headlight Door Diode is in the harness behind the instrument panel, so anytime that the headlight switch is powering the headlight circuits, the HDM "Headlight Doors Open" input is ALSO getting 12v to command the doors open. What testing has also proven is that UNLESS the HDM "Headlight On" input has a path to ground, the doors will NEVER close.

I was simply proposing a solution that would exactly mimic what the HDM "Headlight On" input would expect from a complete stock, operationally sound, headlight circuit. It never hurts to mimic what GM designed as gremlins are a ***** to find and changing anything on one of these modules invites gremlins.

David T.

[Guest Mc_Reatta]

I'm thinking of a possible simpler solution.

We know that the HDM does not need to see 12v at the headlights on yellow wire to raise the lights, only the headlights up yellow black wire at the HDM in an 80s at least. That's how we can have that keep headlights up switch independent of the headlight switch.

I'm going to assume that the 90s HDM would work the same, but this needs to be born out by someone with a 90s HDM. Maybe it wouldn't work and that is why this switch and function was removed in 90 not just due to sprucing up the dash.

Do not wire pin 87a to the relay coil (85 or 86) as proposed earlier.

I propose removing the headlight on yellow wire from the HDM and tape off.

Install new wire at that pin of the HDM. If you get a new pin you can do this without cutting the wire, but if you don't care about that just cut the wire and splice another wire to the HDM side and let the dash side float.

Run that new wire from the HDM headlight on contact to each of the new headlight on relays and connect to the 87a contacts.

Now the 5v retained power from the HDM can not hold the new relays on, and will float when headlights are on. When headlights are turned off, the relays will immediately turn off, turning off the lights, and then that 5v HDM retained voltage will be shorted to ground thru 87a new connection to the headlight filaments and the doors will close.

No need for another relay or high wattage resistor.

Should work fine in an 80s, but someone with a 90s style HDM would need to confirm it will work for them.

Could be made into a plug and play solution but would be a lot more trouble and money. I think I would go with the pull down resistor first and if that could not be tuned to work adequately, then opt for this method, at least in an 80s.

[drtidmore]

Mc_Reatta,

I agree that should work as described. As I stated, I too questioned the need for 12v at the HDM "Headlight On" input. I got a bit too far into the forest to see the tree (ie using 87a on the power bypass relay as the return to ground for the HDM "Headlight On" input once the relay is powered down. All that seems to be of importance for headlight door operation is a return to ground path for the HDM "Headlight On" input, so it certainly seems a reasonable assumption that allowing that input to float while the headlights are on should not introduce any new gremlins.

Now if the damned weather will just cool off a bit here in Dallas, I will get out and do this mod.

David T.

[Guest Mc_Reatta]

Now if the damned weather will just cool off a bit here in Dallas, I will get out and do this mod.

David T.

Feel your pain. Only break in the heat here before dark comes with the thunderstorms which definitely keep me inside.

[2seater]

In the original factory upgrade, the HDM wire is in between the power on and hi-lo relay so the power on relay is not affected by the HDM voltage. The two added relays under the hood could have been configured the same way, power on and selector relay, but the most efficient from an electrical standpoiint, was separate hi and low relays, but, we were trying to avoid relocating the yellow wire for ease of installation of an upgrade harness. Way back in the beginning, when the O.P. mentioned the inability to get the headlights to close, it was suggested to connect the yellow HDM wire to the output (filament) side of the relays. That is what I am proposing to do. The 87a contact is not needed at all. I intend to try this and no harm if it doesn't work. It's at an existing splice anyway.

[Guest Mc_Reatta]

If I understand your idea correctly, it should work as well. Difference would be your HDM would see 12v on that yellow wire when lights are on, rather than float. From what we know that should be the same as the stock wiring does so should work fine.

[padgett]

On wiring: I have been using SilverStars (55w low beam) for over a decade.

[2seater]

I tried spliting the two inputs for the HDM as I outlined, one to hi and one to lo which does not work, at least not completely. It is somewhat confusing but I did read through the headlight module thread and it seems to make more sense. If I understood that thread correctly, one terminal of the HDM reacts to ground and the other needs 12v. I don't know which wire is which, but I can make an assumption based on how it reacts. If the ground wire to the HDM is connected to the hi filament and the 12v wire is connected to the lo beam, the headlights work correctly, if in the lo beam position. They go up when switched on (default is lo beam), and go down when the lights are turned off. If switched to hi beam, there is 12v on the hi beam wire that is seeking ground and the lights stay on and open just fine. The only fly in the ointment is if the lights are switched off in the high beam position. The lights go out, but stay up, no matter how long I wait. They must be in lo beam position to get the doors to close. If I reverse HDM connections so 12v is now high beam, it pretty much reverses the operation, headlights on causes the lights to illuminate, but the doors don't open. Switching to high beam opens the doors, but turning the lightswitch off just shuts off the lights and the doors stay open.

I tried applying 12v to each of the HDM wires and one causes the doors to rise, but the other does nothing. Applying ground to the the original 12v wire does nothing. Applying ground to the other wire, closes the doors. This pretty much confirms the headlight module thread, at least on my '90. It makes some sense of the way the headlights react with the split inputs to the HDM from the hi and lo beam filaments.

I looked at the relay wiring change suggested by Mc, but I don't think I quite get it. It looks like both relays are to be changed to connect 87a to the HDM hot or ground wire? Both of my wires are yellow, no black stripe, but I can figure out which is which. I am now making a guess that the ground "seeker" from HDM is connected to both 87a's and the other wire looking for 12v is left connected to the original single yellow wire from the headlight switch? Correct?

[Guest Mc_Reatta]

I looked at the relay wiring change suggested by Mc, but I don't think I quite get it. It looks like both relays are to be changed to connect 87a to the HDM hot or ground wire? Both of my wires are yellow, no black stripe, but I can figure out which is which. I am now making a guess that the ground "seeker" from HDM is connected to both 87a's and the other wire looking for 12v is left connected to the original single yellow wire from the headlight switch? Correct?

In a word, yes.

I guess in 90 they decided to save a penny and use yellow wire for both terminals on the HDM. They are both from the same source, the headlight switch, so no foul.

You want to sever the connection of the one going to terminal "C" of the HDM which is the terminal wanting to see ground to lower the headlights. You want to leave the one going to terminal "A" of the HDM alone. That one brings 12v to the HDM when the headlights are turned on to raise the doors.

Then connect a wire from the "C" terminal of the HDM which was disconnected above to either pin 87a or 30 of both of your new relays so it will work the same no matter which beam you are using.

I would suggest going to pin 87a since it doesn't make sense to bring 20 amp power to a place where there is no need for it. Just a short waiting to happen. As you noted in your post, it made no difference whether there was 12v on this HDM pin or not. It is only looking for a ground when no voltage is on pin A to lower the doors.

[2seater]

Okay, that sounds reasonably doable with what is already in place. I just need to reconnect the "hot" wire from the dash to the "hot" for the HDM. The "ground" is already cut at the splice, so I will pull the wire out of the loom from the HDM end and no pins need be changed as the length of wire is more than enough to connect to the pigtails from the relays. The 87a connection as now configured, needs to be cut loose from the 86 anyway, so reconnecting to the HDM ground makes good sense.

As a side note, my left headlight has now decided to only go down halfway. It opens fine, but only closes part way, the right side is fine. Both have new crankarms and rollers in the motor. This just started this morning. Maybe a defect in the HDM timing out on that motor? Weird.

[Guest Mc_Reatta]

It's winking at you.

[2seater]

The latest wiring change with the relocation of the ground wire for the HDM to terminal 87a, works great. Turns off no matter which beam is engaged. It turns out the relay socket pigtails I use have enough reach to get to the splice inside the main harness on the left fender, so clip the wire, connect the two wires from 87a of both relays, and tuck back into the harness. Not quite plug and play, but pretty close.

I will look at the winking headlight in the morning. I did get it to close completely once by hitting it with a dead ground, but only once. It goes down smoothly with the handwheel. Odd coincidence it would act up now. It has never done so in the past. From the diagram, each motor is controlled separately inside the HDM, so perhaps there is a fault?