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Follow the flow chart VinnyD posted. It has the same info that I have in my 87 manual. Your car has "Lamp Driver Module" that the ECM uses to control the check engine lamp. I believe it is above the ECM, to the right of the glove box. You will need to check the voltage at the Lamp driver module and follow the path based on what you see at circuit C, which on my '87 is a white wire with a dark green tracer. If you don't have a volt/ohm meter, you can pick an inexpensive one up at most tool or hardware stores
 

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Discussion Starter · #22 ·
Is this little black box behind the glove box and above the ECM the Lamp Driver Module? Does anybody have a pin diagram so I can check it out?
138219
 

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No, I don't believe that's it. The one on my car is a light green/blue color with 4 wires going into it. Looks more like a wire connector than a module, but there are no wires coming out the other side. The wires should be pink/black tracer, white/green tracer, black, and yellow. I'm assuming you have a 305, the V6 may be different.
 

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I would suggest getting yourself a copy of the factory service manual for you car. There is a wealth of information in them especially if you are going to do your own work.
You can usually find them on Ebay. I think some of the parts suppliers sell reproduction hard copies or digital copies on cd format.
 

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The picture you showed was the Baro sensor. Earlier cars had it mounted on the passenger fender, but later years moved it inside the cabin.

Here's a picture of the Light Driver module. It is wrapped up with the harness as it runs above the glove box. You will likely have to remove some of the wrapping tape to get to it. Ignore the yellow connector on mine ( used to install TPI on mine...).

 

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Discussion Starter · #27 ·
Thanks, that helps. Has anybody ever had any luck with trying to rebuild one? It doesn't look like there's much to the little printed circuit inside, a few resistors and capacitors.
 

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The white / green stripe wire should be 12V when the ECM wants to lamp turned on. The Yellow wire should go to ground at this point and the light turns on.

The light driver module switches a 12V+ signal from our ECM to a Ground signal for the lamp. The yellow wire should be grounded when the ECM wants to turn on the light ( or flash it). Before you go repairing it, you might try getting one from a junk yard and just swapping the board.


Another option might be to use an Electronic device to generate the ground signal. I've used these for many of my projects, and it takes a 12V + signal and returns a Ground.
 

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I think I tracked down this board, P/N 12040004.
From the looks of it there is a transistor, a diode, a capacitor and a couple of resistors.
Are there any markings/ part numbers on the parts on your board, Take a good look on the transistor and diode.
 

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Discussion Starter · #31 ·
Thanks, I haven't pulled it out yet, by the time I get home from work I'm beat. I think I'll try to pull it this weekend and I'll check all the components and see what needs to be replaced. There's a guy just down the street that repairs stereos so he should have whatever I need.
 

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Discussion Starter · #32 ·
I haven't pulled mine out yet, by the time I get home from work I'm beat. Planning on doing it this weekend. I think that must be the problem because other than the check engine light being on all the time it runs fine. There's a guy down the street from me that repairs stereo equipment so he should have whatever I need. I found an NOS one for $54.00 but I want to double check and make sure that's my problem first. Found one in Russia for .63.

OOPS, double posted. Sorry.
 

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Discussion Starter · #34 ·
I've purchased stuff from him before, great guy. I just messaged him so we'll wait and see if I have any luck.
 
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