Puzzling Headlight Issue

[revvychevy]

Hey guys, my first time here. Bought a 1995 GMC 3500 a few months ago and all has worked fine up till last night. Had just been driving the truck with the lights on, stopped at a buddy’s house and turned it off for maybe an hour. I started it to leave and guess what. The headlights that had been working fine an hour ago won’t turn on. I turned the switch and nothing. Tried the high beams and they didn’t work either. I got it home and got the volt meter out to do some testing. Often the switches go bad so I pulled the plug on the light switch and jumped the wires for the headlights. Nothing. So that rules out the switch on the dashboard. Hooked the switch back up, tapped into the green and tan headlight wires where they run along the left fender and turned the switch on. They’re both getting 12+ volts when their respective switches are turned on. The truck is running HID’s so I jumped them right to the battery and they turn on, eliminating four HID systems that could’ve simultaneously quit (it’s happened). I figured it might be the low voltage issue that many of these trucks have, which would run halogen bulbs dimly but not HID’s, so then I took some normal 9005 and 6 halogen bulbs and plugged them into the sockets. They didn’t work either. I decided to test the headlight sockets themselves for voltage and, guess what...nothing at all. Checked the ground wires from the sockets with a resistance test to make sure they’re good and they are.

I did the low beam bypass with a relay so that the low beams stay on with the highs a while ago and it’s worked great. We figured maybe the relay or a connection there is bad. Checked and double checked everything with a volt meter, even the relay socket and connections, and everything works fine, eliminating that as a potential problem.

At this point all I can think of is that maybe since its mischief night, somebody cut my headlight wires somewhere between the fender and the headlight socket. It seems like that’s where the current stops traveling to the headlight socket. But a buddy suggested a resistance test on the wires as a last resort, so we tried that. The high beam wire is good. It turned out the low beam wire has no continuity from the socket to a spot near the cab where I could access it. However...the low beam DOES get continuity between the low beam socket and the high beam wire. Which indicates they’re shorted together somewhere. I checked as much as I could see along the wiring harness and don’t see anywhere it looks like the wires are broken or shorted.

Is there something else I’m not thinking of that this could be? Has anyone had this problem or a similar issue with the headlights too? I’ve heard of the headlights on these trucks shutting off randomly and it seems to always be an issue with the switch. Apparently not in this case.

Thanks for your help!! Sorry for the long read. I tried to list all the info I have. Your answers are much appreciated. Have a happy Halloween


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[Eveready]

I'm sure you looked at the fuses but there is one thing you might try. The fuses CAN oxidize in their sockets. I found this out when my radio went out without warning. I pulled the fuse to that circuit, noted that the fuse was intact, and reinserted it. The radio started working again. Obviously there was crud built up in the fuse socket . Its worth a look.

Also the usual culprit in these trucks is grounds. Switching of electrical circuits is usually done by completing a circuit to ground. From the tests you mention in your post you appear to have checked them. Check the hot side of your lights again with a Volt Meter and/or test light. If the hot side is in fact hot then you have a switch to ground issue.

It is possible that the HID lights put too much of a load on the switch. If you are getting lights when you ground the switch then it is most likely the switch itself.

Good luck, welcome to the forum and let us know what it turns out to be.

 

[revvychevy]

I'm sure you looked at the fuses but there is one thing you might try. The fuses CAN oxidize in their sockets. I found this out when my radio went out without warning. I pulled the fuse to that circuit, noted that the fuse was intact, and reinserted it. The radio started working again. Obviously there was crud built up in the fuse socket . Its worth a look.

Also the usual culprit in these trucks is grounds. Switching of electrical circuits is usually done by completing a circuit to ground. From the tests you mention in your post you appear to have checked them. Check the hot side of your lights again with a Volt Meter and/or test light. If the hot side is in fact hot then you have a switch to ground issue.

It is possible that the HID lights put too much of a load on the switch. If you are getting lights when you ground the switch then it is most likely the switch itself.

Good luck, welcome to the forum and let us know what it turns out to be.

Thank you! I’ve never thought of fuses oxidizing so will definitely check that. The HID system is 55 watts which is what the factory bulbs are. From what I understand though, they surge on startup so that could have fried the switch. I’ll jump the wires and run an extra ground to the switch and see if it’s getting power to the lights.

Your help is much appreciated! Thanks again and I’ll keep this updated.


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[revvychevy]

Problem solved! I pulled the body connector, cleaned the contacts well, and three out of four lights came on. Cleaned all the other connections I could find including the switch and headlight sockets themselves and the fourth now works. There must’ve been so much corrosion that the headlights weren’t getting enough amperage to run. Definitely will be carrying a spare switch around just in case though. Thanks for you help!


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[Oldblue98]

Problem solved! I pulled the body connector, cleaned the contacts well, and three out of four lights came on. Cleaned all the other connections I could find including the switch and headlight sockets themselves and the fourth now works. There must’ve been so much corrosion that the headlights weren’t getting enough amperage to run. Definitely will be carrying a spare switch around just in case though. Thanks for you help!


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Thanks for bringing a conclusion back and posting it. Glad you got it figured out.

 

[Eveready]

Problem solved! I pulled the body connector, cleaned the contacts well, and three out of four lights came on. Cleaned all the other connections I could find including the switch and headlight sockets themselves and the fourth now works. There must’ve been so much corrosion that the headlights weren’t getting enough amperage to run. Definitely will be carrying a spare switch around just in case though. Thanks for you help!

I agree with @Oldblue98 .The threads that are "finished" really help when someone else encounters the same problem. Those contacts can become crudded up and quit working. It is interesting that they all quit at once though. Good job finding and fixing it.

 

[revvychevy]

Yeah haha it’s frustrating when someone leaves it with “I’m sure this is going to work, will try it tomorrow!” Thanks for your help!


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[revvychevy]

Soooo....opening up an old thread again. The headlights worked for a while after cleaning the connections. One night they decided to go out again. I noticed when I bumped the dashboard near the light switch with my fist, they’d flicker and come back on. I got home, pulled the dash panel off and one wire was completely broken out of the socket, a couple others were hanging by threads and half of the pins in the socket were really loose. GM connectors. So I spent about three hours and pulled each pin out of the socket, squared them off with pliers, un-crimped them and removed the old wire, soldered extensions onto each wire on the harness so it wasn’t stretched to reach the switch (probably what caused the wires to break in the first place), re-soldered the pins onto the new wires, pushed them back into their respective places in the socket, got a brand new light switch just because, re-assembled everything and TADA! Lights work perfectly.

That is, until a week later. They randomly decide to shut off again. I scratched my head for a few days until one morning I opened the hood with the switch in the “on” position and the lights came on. Closed the hood, and they went off. Opened it, and they came back on. It turns out the hood latch was pressing on the front lighting harness connector (on the back of the drivers side wheel well) when the hood was closed, and when the connector was pushed a certain way, the lights would go out. When it was pulled, they’d come back on. So last week I cut the connector on both sides, soldered six inch extensions between the wires to make up the difference and soldered the wires directly to each other, bypassing the connector completely. One less thing to go wrong. Turned the lights on and they’re as bright as ever.

Until tonight. When the $@*%*~> lights decide they don’t want to turn on in the tractor supply parking lot. Bumped the switch and nothing. Checked the relay, nothing. Jiggled the wiring harness under the hood, and nothing. Some aftermarket gauges that are wired to the headlights (not the dash lights) lit up unlike before, so there’s power to the circuit, but no lights. I used the off road lights to get home, driving on some little-used back roads. But I’m beginning to think the truck is haunted, especially since the first time it happened was Halloween night [emoji23]. You guys have any suggestions? It’s so weird how there have been obvious fixes but none permanently solve the problem. Your help is much appreciated. Thanks!


__
Tim [emoji631]

 

[Eveready]

Some of those previously stretched wires may have broken (or almost broken) inside the insulation . They look perfectly normal but you may be dealing with yet another almost broken wire. Run parallel jumpers across likely suspects and see if the problem clears up. That is my best guess! Good luck and keep reporting.

 

[Nad_Yvalhosert]

Some of those previously stretched wires may have broken (or almost broken) inside the insulation . They look perfectly normal but you may be dealing with yet another almost broken wire. Run parallel jumpers across likely suspects and see if the problem clears up. That is my best guess! Good luck and keep reporting.

It's good that you have a suggestion to help fix this issue, but O.P. posted this over 4 years ago. It's likely that it has been fixed long long ago. Dates on posts matter.