What circuit tells the BCM to dim the CRT

[Ronnie]

Which circuit tells the BCM to dim the dash lights and CRT when the lights are turned on? Is it one coming from the headlights? Parking lights or what? My dah lights and crt only dim when the fog lights are on.

Thanks!

[padgett]

That is usually caused by a dirty headlamp switch.

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">That is usually caused by a dirty headlamp switch. </div></div>

I have been working on it today and have found that sometimes it will work when pushing the parking light button on the headlamp switch. Can you tell me how to go about removing it and cleaning it.

Any help would be appreciated...Thanks!

[padgett]

I just sprayed tuner cleaner and lubricant in the cracks - mine has worked fine since.

[Ronnie]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I just sprayed tuner cleaner and lubricant in the cracks - mine has worked fine since. </div></div>

Do you mean spray it all around the buttons and sliders without removing the switch panel?

[Howard]

I got my 89 in 1998 and the dash lights would not dim, nor would the buttons light up. I took a can of WD40, with the thin red tube that you can attach to the nozzle, and sprayed between all of the headlamp switch buttons while pressing them on and off. To date, I've never had the problem again. Many have questioned my use of the WD40 as opposed the contact cleaner, but my results speak for themselves. The problem I have with some, note I said some, contact cleaners is that they can dull or melt the plastic buttons. WD40 can not. Also another problem, is that sometimes the photocell in the top of the dash fails with age, which can cause the dash lights and CRT not to dim as well. I would try the switch cleaning first.

[Ronnie]

Thanks for your advice Howard. I'm going to give it a try tommorrow. I think that will probably fix it. I have found that the crt and the dash lights will dim sometimes when I turn the lights on and off repeatedly. Makes sense that a dirty headlight switch would be the problem.

I had the problem with the photocell also. To fix it, I removed the glove box and disconnected the wht/blk wire at BCM connector 3D8. To prevent getting a code B119, I installed a resistor (either 200k or 2 meg, I have forgot) between the BCM connector 3D8 and the BCM ground terminal. It worked great after that when I turned on the fog lights but still would not dim when turning on the park or headlights. So now I'm troubleshooting the light switch.

I know it would have been better to replace the photocell but I didn't want to take a chance of breaking my dash pad or the defroster grille. Both of them still look like new.

[Howard]

Actually, you touched on a point I forgot to mention. If the dash lights and CRT dim when the fog lights are on, then the H/L switch indeed is bad. If the photocell was shot, the lights would not dim with the foglamps.

[Ronnie]

Thanks for all the help. You guys saved me the cost of a new switch. After one cleaning my headlight switch is back to almost 100%. It is still sticking a little. I'm going to give it another cleaning tomorrow if it still sticks after soaking over night.

I love this forum!!

[Howard]

The folks here are sort of like Radio Shack. You have questions, they have answers. The big plus? It's free <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />

[Guest kennyw]

I have to disagree with all of the above: I have had a few switched of the 88-89 years apart. There is nothing a cleaner can clean. You can use a small file on some of the headlight contacts. There is also nothing you can do for the slider dimming switch. Just nothing to clean. A small drop of oil on the bar the slider knob slids on does help the slider to move freely.........Your, [no dimming] is the light sensor in the middle of the dash not working. Go to a bone yard and pull a few from wrecks. You will see it pulls straight up and out like the small yellow bulbs. Now with this knowledge you know how to get your sensor out. Good luck on not breaking the grille cover...........If your crt and dash are now dimming it is just because the sensor has decided to work for a while. It will stop working and you will sone replace it.........ken

[Ronnie]

Your response seems to be Elementary, my dear Watson. <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" /> It appears you have not carefully read this entire thread.

I determined that the photocell needed replacement. But I choose to bypass the photocell (see post above) in order to keep from breaking the grille cover. After that is when I started to investigate the dimming problem.

The facts speak for themselves as to whether of not spraying with WD40 works or not. I went from the dashlights and crt not dimming at all when the headlights or parking lights were turned on, to them working perfectly after two sprayings with WD40. I don't see how you can disagree with that at all. As for the photocell being the problem, it was disconnected and replaced by the proper resistor to simulate a dark condition at all times to the BCM before I started troubleshoting the dimming problem. Therefore the photocell could not have been, and is not currently, working erratically.

I believe the problem WD40 may correct, is more of a sticking problem in the switch than a dirty contact problem. The switch now feels more crisp when the buttons are pushed and it seems to snap on and off.

One thing is for sure, spraying with WD40 (no contact cleaner), as Howard and others have suggested, definitely worked for me.

Thanks to everyone for all your help!

[Howard]

While I don't like to disagree with anyone on the forum, I can say that the switch problem is a common one. The cleaning fluids seem to fix it. This advice has been followed more than once and the problem has been solved for a number of board members. However, if the lights do not dim with the fog light switch, then I will agree with you that the photocell is shot. As to why this "cleaning" works, I don't know. I've never taken the switch apart. I also agree that spraying the slide control does nothing. The problem seems to be in the push button part of the switch. The rule of thumb I use to discuss the dimming issue, if the dash dims with the fogs and the photo cell covered up so there is no daylight hitting it, then it's the switch. If they don't it's the photocell. I stand behind my cure, sorry.

[Guest Fla88Coupe]

Back to this issue again.

The back light for all of the buttons does not come on when the head lights or parking lights are turned on. I can not adjust the CRT intensity because it states that the adjustment can not be made in day light even though I am attempting to perform this operation in the dark. It seems that the BCM thinks it is daylight all of the time. I entered service mode and reviewed the data and found that the Photocell output in the dark was 48 while reading 12 in daylight. the range, as I understand, is 0-99 with 99 when it is dark. In overide mode, the level is at zero BI04, I believe. The backlighting works when I overide and the lights work during the self test on startup.

My conclusion is that the Photocell is bad, telling the BCM that it is daylight all of the time. If this is the case, how do you remove the cover to get to the photocell without breaking it? Where do I find a replacement part?