In dash lighting malfunction?

Tiny
AUTOANSWER500$
  • MEMBER
  • 1992 CADILLAC FLEETWOOD
  • 4.9L
  • V8
  • 2WD
  • AUTOMATIC
  • 150 MILES
All of a sudden, I noticed I did not have lighting at my information center, A/C control, fuel data center. I was told my BCM could be defective. I replaced it with a remanufactured one and still had the same problem. I am somewhat familiar with the BCM, I replaced the same one a little over two years, I had driven the car seven years prior to that without any issues. Earlier I meant 150,000 miles. Thank you
Wednesday, August 30th, 2023 AT 6:31 PM

9 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,641 POSTS
I would start by checking the fuses this guide can help:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

If the fuses are okay here is the pin out for the BCM and a guide on how to check them.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Check out the images (below). Please let us know how it goes.
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Thursday, August 31st, 2023 AT 12:52 PM
Tiny
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Hello Ken, thanks for responding, I checked fuses at the driver's side under dash, checking the pins at the BCM, would be a little more detailed, I suspect you mean checking the 2 harness plugs, with the key turned on to see if I'm getting power to those pins, I don't really understand or know where to start, is there more one on one available as far as instructions. When I first turn the key on, I get illumination but it's very dim, and then it just goes away, the car starts and drives fine, but because of my issue I'm not able to read the on-board diagnostic center.
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Thursday, August 31st, 2023 AT 2:56 PM
Tiny
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Hello Ken, or is there anyone else that's able to respond?
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Friday, September 1st, 2023 AT 8:28 AM
Tiny
KEN L
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I will post this in our expert forum to see if anybody else will chime in.
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Saturday, September 2nd, 2023 AT 9:59 AM
Tiny
AL514
  • MECHANIC
  • 5,257 POSTS
Hello, since you have the digital instrument cluster with the Fuel data center, climate control, etc. There is this 16v Reference that goes out to all those devices(modules) on an Orange/Black wire from the BCM, it's a strange setup, I remember working on one of these old Caddy systems. But check for those 16-volts on the C2 connector pin D13. And then on circuit 44 Park Lamps dark green should be a 12volt feed from Lamp Switch either on the Park lights or Head lights setting. These older 16volt Ref. I believe there is a step-up transformer that provides the higher than battery voltage. I'll post the older diagram I was looking at.
This 3rd diagram looks to be a continuation of circuit 44 dark green wire from diagram 2.

And if you're having multiple BCM failures, I would load test the Grounds for the BCM (4th diagram) Powers and Grounds.
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Saturday, September 2nd, 2023 AT 11:59 AM
Tiny
AL514
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Did you also lose lighting to the Radio, Lamp Switch itself, Window Lockout switch- I assume on the door switch, etc?
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Saturday, September 2nd, 2023 AT 12:42 PM
Tiny
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No, I did not and thanks for your help it was greatly appreciated, I luckily found it.
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Monday, September 4th, 2023 AT 6:53 AM
Tiny
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Yes, I returned the BCM, and decided to stick with the issues at hand, temperature and fuel control modules only, it only takes one to show them both defective, I started with the temperature control first, they both lit up and started working fine, my suggestion to anyone who plans on keeping or restoring an older vehicle to do what I did in advance, invest in another used vehicle close to the same year, same model, and have parts at your disposal as they become scarce. As far as the BCM, it was only 140.00 dollars brand new. I did not want to take a chance not knowing everything about the parts vehicle and luckily even the new one did not make a difference. I hope this genuinely helps someone.
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Monday, September 4th, 2023 AT 8:08 AM
Tiny
AL514
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What was the issue you found? It helps with future cases; I know some of these older Caddys are still around. They seem to last if taken care of.
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Monday, September 4th, 2023 AT 8:09 AM

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