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Old 02-10-2019, 03:48 PM   #1
Jmoney01
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Dash lights

I have a 1980 gmc. For some reason the dash lights quit. Does anyone know the color wire that comes from the light switch? Figured I'd start there and trace it out.

Thanks
Jeremy
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Old 02-10-2019, 05:49 PM   #2
kipps
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Re: Dash lights

Quite sure it's a gray wire by the time it gets to the instrument panel connector. Should be the same at the headlight switch, but can't guarantee that.

The headlight switch can be disassembled, but do so very carefully. There's a lot of little parts in there. I got a bunch of pics of how it goes together if you open it and get stuck.

There's several separate switches in the headlight switch. The main incoming wire goes through a thermally operated circuit breaker, then is switched onto the park lights and headlights. You'll see a small jumper going from a park light hot to the variable resistor for the dash lights. The last switch connects the white wire to ground to illuminate the dome and courtesy lights.
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Old 02-11-2019, 12:48 AM   #3
Dead Parrot
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Re: Dash lights

Double check the fuse for the running lights. Had an Impala where the dash lights and running lights were on the same fuse. Brake/turn were on separate fuse.

Also possible the rheostat for the brightness adjustment has gone out.
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Old 02-11-2019, 06:52 AM   #4
Jmoney01
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Re: Dash lights

The rheostat is in the light switch isn't it? If I dont have power to the gray wire I will just replace the switch and see what I have. Went through all the fuses yesterday
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Old 02-11-2019, 08:14 AM   #5
Jmoney01
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Re: Dash lights

Checked for power.... I have power to the dash. It would have to be in the circuit behind dash then, correct?
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Old 02-11-2019, 11:29 AM   #6
Dead Parrot
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Re: Dash lights

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Originally Posted by Jmoney01 View Post
The rheostat is in the light switch isn't it? If I dont have power to the gray wire I will just replace the switch and see what I have. Went through all the fuses yesterday
Yes on rheostat. After a few decades, they get a bit twitchy. Mine is down to two options, full bright or off. And full bright is getting harder to get.

If you can snake a hand up to the cluster connector, might try gently rocking it and make sure it is still fully seated.
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Old 02-11-2019, 12:11 PM   #7
kipps
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Re: Dash lights

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Originally Posted by Jmoney01 View Post
Checked for power.... I have power to the dash. It would have to be in the circuit behind dash then, correct?
Uh... Define your terms. "Dash" refers to the all-encompassing chunk of metal and plastic in front of the driver and passenger. "Instrument cluster" or "instrument panel" is the molded plastic piece that contains the 5 or 6 gauges.

Quick first check. Do any lights come on with the headlights at the radio or heater controls? If so, the gray wire circuit is working correctly from the headlight switch.

If you pulled the instrument cluster out of the dash, and unplugged the connector from that, you should get 12 volts on the gray wire when the headlights are on. If the instrument panel lights still don't work, it could be one of three problems.

#1, the printed circuit on the back of the instrument cluster is defective. I would remove the instrument cluster from the vehicle, and check it closely for problems. Both visually and with a multi-meter.

#2, you have a bad ground connection. The ground on the instrument cluster should be a black wire. There might be more than one. I'd assume if your gauges are still working correctly, you don't have a ground issue. But depending on which printed circuit you have, it's possible the grounds are separated by task.

#3, all the light bulbs are blown out, and just need to be replaced.
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Old 02-11-2019, 05:52 PM   #8
Jmoney01
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Re: Dash lights

Yes, the cluster. I have power to the gray wire at the plug. I picked up a couple of bulbs today to check that out. Is the printed circuit available or is it a junkyard find and hope it works?
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Old 02-11-2019, 06:08 PM   #9
TKCR
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Re: Dash lights

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Originally Posted by Jmoney01 View Post
Yes, the cluster. I have power to the gray wire at the plug. I picked up a couple of bulbs today to check that out. Is the printed circuit available or is it a junkyard find and hope it works?
The printed circuit can be gotten at any of the truck places, like LMC and such.
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Old 02-11-2019, 07:20 PM   #10
kipps
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Re: Dash lights

Use the ohm settings on your multi-meter to check for conductivity on that printed circuit. If you find a visual problem, I'd love to see a picture of it. I've wondered how they fail when they do.

If you replace the printed circuit board, I would visually compare the printed circuits to make sure they still go to the correct pins on the connector. If not, it's pretty easy to move the pins around on the instrument cluster connector.
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Old 02-11-2019, 07:32 PM   #11
Jmoney01
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Re: Dash lights

I will pull cluster and check it out. The napa guy said he fixed his once using a rear window defogger repair kit. That made sense. If I see the issue, it's worth a shot
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