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Chasing electrical gremlin?


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I'm working on trying to find out why my tail and brake lights aren't working on my Wildcat. I took it for a spin today to try to work out kinks in the new carb setup and realized that from behind only the turn signals work. I have no voltage at the rear harness in the trunk. When I checked with a test light with "key off" the light was on at the brake signal fuse. Isn't this switched? What could cause this?

Mike

BTW, the Qjet was very smooth. Not as much low end pickup but I will continue tweaking. Also it doesn't appear to be running rich, apparently outside it doesn't smell like gas as much, go figure.

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I would say that the brake light circuit is not switched, and should work without the ignition on. Also I would say they are not working because the grounds are compromised. You might try just loosening the grounds in the trunk and then tightening them again. If the lights work then you gotta take em apart and clean the grounds thoroughly.

JD

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REMEMBER . . . the brake light circuit goes through the turn signal switch on its way to the rear of the vehicle. IF something is not "right" inside the switch, although the turn signals might work (as on the front but not the rear), then you'll need to check the connector where the turn signal harness mates with the vehicle's wiring harness at the base of the steering column. On the later connectors, the brake light wires are on one end of the connector (which is flat, but might be similar if the connector is circular, as many of the earlier ones were)--it might look like it's plugged in "good", but it might not be.

Then, there usually is a junction block plug-in near the rear wheel area, usually driver's side, where the body harness mates to the rear lamp harness. There's usually nothing wrong back there, at that connector, as it's in a place that is pretty well hidden (typically) and no one knows it's really there to mess with.

As for grounds, there usually is one on each side of the vehicle, front AND back, for the lamp harnesses. But one ground would not usually keep both sides from working as each side has its own ground.

From experience . . .

NTX5467

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Aargh. I'm afraid the rigging the high school kids did on this car continue to the electrical system. There also seems to be an awful lot of really crunchy wires. Not burned, just old.

Still no brake lights or tail lights. I jumped the two wires at the brake light switch and no luck. I don't think this could be a grounding problem because the rear turn signals do work and are bright. How do I test for a short? I can't see that jamming a sharp prod into an insulator is really that good of an idea.

On a happier electrical note, I just finished installing a Secret Audio in my friends 60 Electra. I think their product sounds good, but their customer service is crap. Also, I beat myself up about not being able to get the memory wire going, I call customer support, "Oh, those wires aren't labeled correctly, switch the red and yellow wire." GDitall. Sometimes I wish I could just throttle a dude over the phone. While I'm at it, do you guys know that you CAN'T play an ipod through this system without the $250 ten disc changer? Why would you need the changer if you are going to listen to the ipod? Or vice versa.

It sounds good though and he didn't have to hack the dash. Plus this is the last thing I had to do so I can finally get paid for fixing all of his stuff (after having it for almost a year). Apparently, I'm slow. <img src="http://forums.aaca.org/images/graemlins/blush.gif" alt="" />

Somebody gimme a hollar if you can think of something else to check before I order a wiring harness. Please don't make me do that.

Mike

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Rather than a "short", what about an "open circuit"? If there was a short, you'd find a cooked fuse in that circuit, from which you could put a bigger fuse and look for where the smoke was coming from (before it got tooooo smokey!!).

On most connectors, you can "back probe" the connector and not damage the wire's insulation, as a general rule, unless it's one of the more modern "sealed" and "snap-together" weatherproof connectors. Many persons have been known to use the test probe to pierce the insulation, which should not cause any real issues in the near future, as the insulation should have enough resiliency to close up the probed/sliced area. Or you could put some elec tape around the wire and seal it up, hopefully. Still, if you can "back probe" the terminal in the connector, that would be the best way to do it.

Enjoy!

NTX5467

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I ran into a similar problem with my Skylark.

It all began when I replaced burned out lamps in the tail lights... then the fun began... all manner of odd gremlins appeared and changed depending on which electrical circuit was on/off...

I think your car is the same, but on my '65, lamp grounds go to the body via the lamp sockets. My first clue of what was wrong was when I observed that the bulbs would remain lit when the sockets were removed from the lamp assmebly. Scratch head for a while and it dawns on me that somewhere, the harness is grounding via another light circuit. Took harness apart at the rear body connector and tested contacts for continuity with the mulimeter. Voila! There was a 'leak' between left and right brake/turn circuit and the rear lights. Very careful inspection of the rear harness found an area of the bundle that had been overheated when the left rear clip was cut out to repair collision damage in the distant past. New harness from M&H was about $100 and solved all the problems.

I'd recommnend some intense circuit testing to see if you have continuity (short) where you shouldn't. Be sure to test for shorts with the bulbs removed, they will provide a closed circuit if left in. My 'research' bore fruit when I finally realized that the bulbs were still in the tag light and the backup lights.

Other things to keep in mind about our old Buicks is that while the plastic insulation is 'electric proof' and highly <span style="text-decoration: underline">moisture resistant</span>, over time, the insulation does become brittle and moisture passes thru the insulation creating oxidation on the copper conductor inside. In turn, this increases the resistance of the wire throughout the circuit. The wire oxidizes on the outside, which is also the path of the electrical current... it doesn't run 'inside' the conductor. A circuit drop of 2-3 volts is not uncommon as a result (dim bulbs, radio problems, high circuit drain from power options, etc).

New wiring is wonderful...

Good luck with your gremlin hunt.

Cheers,

JMC

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<img src="http://forums.aaca.org/images/graemlins/confused.gif" alt="" /> OK. I was in the garage for at least five hours today.

I took the turn signal switch apart and cleaned it. Changed the light bulbs in back. Took the harness at the firewall apart, cleaned it. Still no lights.

Now I have no dash lights, and the vent blower isn't working. (They might not have been working when I started this project, I just noticed it today.)

There is no voltage at the fuse panel for the dashboard lights. Fuse is fine.

Front of car still has all lights working. Radio works. Rear turn signal works. All other interior lights work with door switches and light switch. Conv. top works. Battery is strong.

I will try reading my shop manual even more tonight. I'm afraid I've exhausted my knowledge of electrical testing.

Time to buy an Impala. <img src="http://forums.aaca.org/images/graemlins/mad.gif" alt="" />

Mike

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Time to buy an Impala. <img src="http://forums.aaca.org/images/graemlins/mad.gif" alt="" />

Mike </div></div>

Don't do it Mike. I know electrical issues can be tough (I trained as an electrical engineer and I dislike automotive electrical gremlins), but please don't resort to procuring an inferior product.

Worst case, you could always take it to a shop that will deal with it.

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Sometimes a bad bulb in the front, or anywhere, in the circut will cause a back feed and make the rest of the bulbs in the circut do weird things. If one filament blows in a bulb and part of it lands on the other filliment it can cause a backfeed and light bulbs that are not suppose to light, and cause other bulbs that are suppose to light, not light. Also, other bulbs may be dim. Been there and done that! As you are going though the circut and testing the wires start at a point that you do have power and systematically work your way back to the point that you do not have power. Pull on the wires as you go and see if they pull apart or feel spongy in a spot as you go. If it is, I garren gum T that's where the problem is. You will find a green spot that will no longer conduct. Too bad I wasn't in Texas or I would look at it for you myself. Good luck, Never gots an A fer spellin. <img src="http://forums.aaca.org/images/graemlins/crazy.gif" alt="" /> Dave!

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Well, it looks like you're continuing your restoration into the electrical circuitry of the vehicle, too, which can also expand your knowledge of the vehicle in that area. Plus narrowing down the areas in which to look for the "issue".

The blower should be on its own circuit and harness (the heater-a/c harness). The turn signals will "branch off" from the main feed circuit for them, going to the front and back with their own respective "lamp harnesses", but the brake lights will be in that mix for the chassis harness and the rear lamp harness. Similarly, the "instrument panel harness" would be a separate entity too. At least these would be separate items if you were looking for them in the GM parts book.

Getting an Impala, as jokingly as that comment might have been made, would not really solve anything as most of the GM vehicles would wire the same (same color codes and such, too) as those things would have been more in the realm of Fisher Body than particular GM divisions (as such) back then, I suspect. Hence, you might as well find your problems with what you have rather than acquire some new ones, with all due respect.

I had some intermittent issues on one of my cars, electrically, several times. The first time it was with the main feed to the ignition switch. I fixed that one and discovered a prior owner had used that wire for a power lead for something that was not there anymore, leaving a wire with a stripped section covered with the beloved chewing gum foil. I fixed that and then, later, that same wire had an issue at the bulkhead connector (inside, luckily!), with the terminal being a little too loose on the terminal from the outside--sudden "no start" conditions (i.e., no starter working!). And then the hidden corrosion on the battery terminals came later.

Methodially working through the circuits, including checking for flaky terminal connections, can also be a reminder of how great it is to have the really full-sized front floorboards and bench seats of those older (and much more spacious) vehicles' interiors.

NTX5467

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My day today was spent moving crushed granite around in my front yard, Ya know, real relaxin'.

The Impala part was just the frustration of continuing to have to WORK at a restoration rather than being "credit card guy" and paying for a new harness with all of the proper ends and such. Last night I went to the book store to get an electrical wiring problem book and today I bought some more diagnosis tools to try some other options. I'll try one more day and then probably take it to a "pro" who can rig it faster. I realize I won't be happy, but at least he can fix it and I will unrig it.

Thanks for all of your help.

Mike

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Make sure you have the correct bulbs in the right spot. 1157 for dual sockets and 1053 for single if you mix this up you can have some real interesting problems. My buddy switched the wrong tail bulbs out and every time he hit the brakes the dash lights would come on but he did not have brake lights. Just for grins this was on a Chevelle.

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  • 1 month later...

A couple of vagabonds (BS & OT) dropped by the other day after spending some time at the Lonestar Roundup hotrod show.

Uhhh...three words. BRAKE LIGHT SWITCH. I still don't have taillights, though. I have swapped out the headlight switch for a known good one and still no dice. I will try something else later tonight.

Mike

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  • 2 weeks later...

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I'll try one more day and then probably take it to a "pro" who can rig it faster. </div></div>

Update:

OK, so I haven't taken it anywhere yet. The cool thing about going over it yourself is I'm finding all sorts of other things that the "pro" wouldn't have even known/ been paid to look for. Like the courtesy light switch that never worked, or the glove box light. Both come off of a harness behind the glove box. The courtesy light wire had been cut, then spliced on the wrong side of the cut (DUH). Glove box light at best could be described as a rat's nest, and that's just the picture of it in the manual. They're both working now. I'll keep on chasing down the taillight/ dashlight issue myself I suppose. Or bring some test equipment to Salado this weekend <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />.

Mike

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  • 6 months later...

It's baaaack.

I had a buddy come over today.

We checked all continuity in all of the wires. All good.

Brake lights worked when 12 volts applied- ground OK.

Took apart headlight switch (again) worked as it should.

Tried headlight switch while out of dashboard.......................

When I replaced the interior trim pieces around the bottom edge of my dash, apparently, I neglected to install the nut that grounds the headlight switch to the dashboard. cry.gif

BINGO grin.gif

I'm legal now.

My rear end (differential, not butt) is gone, bad noises. Lots of free play when jacked up.

One thing at a time.

Later,

Mike

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