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Dash lights/Old Truck

1994 GMC 2500
Dash lights went out. Where do I start. Electric is my least favorite.
The lights for heater control have been funky from the beginning. When I start the truck the blink until the truck warms up? after 15-20 minutes they come on and work right. Now the dash light went out. Also, when I turn the headlights on the lights for heater control go out. Black screen. This also happens after the 15-20 minutes, Where do I start

Yikes. I hate electrical problems too.

Is this truck in good condition or is it a beater? If it’s a beater, you could install and wire a new light under the dash that illuminates the gauges.

Hopefully, someone else will offer a better suggestion, but this is a hack solution to a problem I once had many years ago on an old beater I was driving. I used the same solution to get my parking lights and tail lights working as well, by installing and wiring marker lights to a switch mounted under the dashboard.

One possibility is a bad chassis ground. Given the age of the truck, there may be a corroded ground point.

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Could be a bad headlight switch. That might explain the intermittent on/off.

@Triedaq is probably right. Finding the bad ground is the hard part. What I’ve seem is that a bad ground will often cause some things to light when they should not, some gauges to show very strange readings, or things to get dim and bright at odd times.

You need to get an electric schematic and at least identify the color of ground wires on your vehicle, then you have to crawl under the dash and start following wires, and cleaning contacts. This is not fun.

Have you ever had a flashlight that stops working, and you remove and install the same batteries, then it works? That’s what’s happening to your dash lights I expect. You’ve got some corrosion built up somewhere – likely at various places – in the circuit. The reason it seems to work better after things have warmed up is b/c metal expands with temperature, and that creates enough extra force between the two parts to make a better electrical contact.

Probably where to start is connecting a volt meter to the two wires going to the dysfunctional bulb, and watching what it measures as you jiggle stuff around, and turn on other lights, etc… If it measures the same, and enough to light the bulb, then the problem is in the contacts at the bulb itself. Or the bulb. I’m betting tho that the voltage will vary, and that means there’s unwanted resistance (poor electrical) ahead of the bulb somewhere. Or behind the bulb (the ground connection.) Metals are excellent conductors, but metal oxides aren’t. And metal oxides form on most metals over time just from the oxygen in the air.

Trying to figure where all this oxide problem is located without a wiring schematic is sort of like finding yourself in a city you’ve never been in before, late a night, without a map. Problematic. So the first order of business if the bulb contacts aren’t the problem is finding a wiring schematic for your truck. then you can hook up your volt meter and start probing where the voltage is disappearing. Usually once you find the problem spot, you can scrape the oxide off with a pen knife. But having a can of contact cleaner is very helpful and saves time too; no electric technician would delve into this without a spray can of contact cleaner on hand.

I agree with Mustangman about the headlight switch.

Bad fuse. Replaced fuse. It blows when I turn the lights on. I did replace headlight switch to no avail

That means there is a short somewhere, probably in the wiring from the fise to the lights, but it could be in a light socket or connector.

Update: It seems to be not when I turn on the lights, but when I turn the dimmer switch up.
I turn the lights on with the dimmer switch down towards dim, Then as I turn the dimmer up towards bright…it blows the fuse. I just went through 5 fuses. I can actually hear the fuse pop (blow)

Bad dimmer switch? I just replaced the headlight switch :rage: had that all apart already

Its a beauty. Clean and been garaged. I have no taillight issues. Just the dash lights. I just learned that it blows the fuse when I turn the dimmer switch from dim to bright…

Replaced headlight switch. No help. Just learned dash lights blow the fuse when I turn the dash lights from dim to bright. Do I need to replace the dimmer switch?

Sure looks that way.

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Dang it. Not the dimmer switch either. I think I’m going to alternative
lighting

Does this truck have an aftermarket radio?

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Yes it does

Disconnect the radio, the illumination circuit is probably wired incorrectly.

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What’s your address. I owe you a Christmas card! Lol…

I unplugged the alpine cd player that is mounted under the seat. I Have
Dash Lights!

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It only works with the dimmer all the way up, but that’s a huge improvement