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Discussion Starter · #1 ·
Hey guys, so as the title says once I illuminate the park or headlights on my '95 Caprice the entirety of the dash lights go out, including the speedometer and odometer and radio. I tried pushing that little "dark mode" light bulb symbol switch to the lower right side of the radio and that did nothing. Also tried a different headlight switch out of another 9c1 Caprice with no difference. What could the issue possibly be?


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Nothing to do with Stealth Mode.
By the selector that turns the parking / head lights on / off, is a thumb wheel that adjusts brightness.

Every time I hit a curb or pothole hard enough, I had to play with that thumb wheel again to get the lights to come back on.
More to the point, I had to wiggle it side to side WHILE moving it as originally intended.

I never truly fixed the root electrical frailty, as I could always get it to work again.
For whatever it's worth, this happened to me in 3 9C1-LT1s AND a civi Caprice wagon (all of which I dearly miss).
Hope this is of some help.
 
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Yessir, I did that. No luck.
Sorry I had to be sure.

Also tried a different headlight switch out of another 9c1 Caprice with no difference.
Assuming that both headlight switches are good (not worn out) it comes down to a blown fuse, bad wiring, or a damaged dimmer module.

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Did you just get the car or is this a new problem?
Has a aftermarket radio been installed?

If you blew a fuse or damaged the module you will have to find out what caused the problem(short to ground usually).

This is the circuit diagram:

The "instrument panel dimmer module is where I would start. There should be +12V on the yellow wire.
The green wire from the head light switch dimmer wheel should have 0-12V as you turn the wheel(from my memory).
The gray wire should also have 0-12V as you turn the wheel. If The radio,speedo, and climate control lights do not work I expect 0V on the gray.
 

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Discussion Starter · #6 ·
Nothing to do with Stealth Mode.
By the selector that turns the parking / head lights on / off, is a thumb wheel that adjusts brightness.

Every time I hit a curb or pothole hard enough, I had to play with that thumb wheel again to get the lights to come back on.
More to the point, I had to wiggle it side to side WHILE moving it as originally intended.

I never truly fixed the root electrical frailty, as I could always get it to work again.
For whatever it's worth, this happened to me in 3 9C1-LT1s AND a civi Caprice wagon (all of which I dearly miss).
Hope this is of some help.
Sorry I had to be sure.


Assuming that both headlight switches are good (not worn out) it comes down to a blown fuse, bad wiring, or a damaged dimmer module.

View attachment 206510

Did you just get the car or is this a new problem?
Has a aftermarket radio been installed?

If you blew a fuse or damaged the module you will have to find out what caused the problem(short to ground usually).

This is the circuit diagram:

The "instrument panel dimmer module is where I would start. There should be +12V on the yellow wire.
The green wire from the head light switch dimmer wheel should have 0-12V as you turn the wheel(from my memory).
The gray wire should also have 0-12V as you turn the wheel. If The radio,speedo, and climate control lights do not work I expect 0V on the gray.

Awesome. Thanks guys, I'll try to check it out a bit further this evening and see what happens. Pretty much I got this car as a rolling shell but the guy included the original engine, he was intending on parting it out but I saved it from that, outside of testing out the engine/trans transplant I haven't done any actual driving with it yet. Hoping it's the dimmer wheel instead of a deeper issue. I now remember my brother's 1990 9c1 had a similar issue with the dimmer wheel. As for the radio? I swapped in a 1995/96 GM Cassette/AM/FM radio out of, I believe, a Blazer. Seems to function fine. If the dimmer wheel doesn't seem to be the problem I'll plug out the radio and pop in a am/fm radio out of a 1994 Caprice and see if that fixes anything. And if all else fails I'll dive deeper. Cheers again guys.
 

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Hoping it's the dimmer wheel instead of a deeper issue.
Also tried a different headlight switch out of another 9c1
I would suggest testing versus time and cost of continued swapping.
The "wheel" can also be tested out of the car with the Ohm function of a multimeter.

I now remember my brother's 1990 9c1 had a similar issue with the dimmer wheel.
The systems are different. The 1990 runs all the instrument light power through "the wheel" This allowed heat and wear to be a issue. The dimming module removes heat from the switch area but as MD experienced wear can still be a issue.

I swapped in a 1995/96 GM Cassette/AM/FM radio out of, I believe, a Blazer. Seems to function fine. If the dimmer wheel doesn't seem to be the problem I'll plug out the radio and pop in a am/fm radio out of a 1994 Caprice and see if that fixes anything.
I have not personally experienced a GM radio that has matching connectors (plug and play) that would damage the lighting circuit. If the radio has malfunctioned unplug it then check the instrument fuse.
My question was to check if the wires to the radio had been cut and/or spliced witch is a common source of instrument light problems.

Fresh from service cars can be the victim of agency modifications to interior lights, horn, audio system, and other circuits. Past owners can also cause problems with aftermarket audio, security, and remote start systems.
 

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9C1-9C6 Fan - I tried to look but I did not see where you live. I had this problem with my '96 Caprice. I live just East of Pittsburgh, PA where there is rust and salt in the winters. My problem was that the radiator core support rusted on the passenger side so the ground was going bad. You might take a look and see if you have solid metal for a good ground. Until I could find a replacement radiator support, I ran a new ground wire to the frame so that I had headlights.
 
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