Headlight in 69 C10 quit working - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Arl37 · 02-21-2020, 10:57 PM

Tail lights, brake lights, turn signals and parking lights work but headlights quit working. I've read all the threads on this subject and pretty much know what to do to diagnose the problem with two exceptions.
I recently installed the headlight relay system which is supposed run the headlights directly from the battery and only use the headlight switch to trigger the relays.

First question. In checking the headlight switch how much voltage should be going to the dimmer switch. 12V or something less that because the headlights are not powered by the headlight switch anymore?

Second question. Anyone experienced loss of headlights as a result of adding LED Tail lights , parking lights and the appropriate LED turn signal flasher.

**dmjlambert** · 02-22-2020, 03:07 PM

The whole system works on 12v, so you should have 12v at the switch. With engine running it could be more, such as 14V. Most likely problems in a headlight not working situation are bad relays, bad hi/low beam switch, and burned out headlight bulbs, and burned out fuse (if the relay harness has a fuse). Are both high beam and low beam not working? I recommend using a probe type test light or multimeter to check if you're getting voltage at the relay, and voltage at the headlight. You can use an alligator clip test wire to bypass your wiring and check if the headlight bulb works. If you have the type of relay harness that plugs into the factory harness at the headlight connector, you could just unplug the relay harness and plug the factory headlight connector into the headlight and see what you get. I don't think it is likely LED tail lights, parking lights, and flasher module would affect headlights.

Andy4639 · 02-22-2020, 10:59 PM

Check the dimmer switch first thing. Take the wire connector loose and see if you have power on it.
Dimmer switches are know for headlights to not work.

franken · 02-23-2020, 08:29 PM

Yes, dirty contacts on the dimmer can cause this. Cycle the dimmer switch a bunch of times. It's worth a try and free.

Rick Bollinger · 02-23-2020, 10:32 PM

After dimmer check your grounds directly at the headlights

02-21-2020, 10:57 PM	#1
Arl37 Registered User Join Date: Jul 2011 Location: Valley Center, Ca Posts: 277	Headlight in 69 C10 quit working Tail lights, brake lights, turn signals and parking lights work but headlights quit working. I've read all the threads on this subject and pretty much know what to do to diagnose the problem with two exceptions. I recently installed the headlight relay system which is supposed run the headlights directly from the battery and only use the headlight switch to trigger the relays. First question. In checking the headlight switch how much voltage should be going to the dimmer switch. 12V or something less that because the headlights are not powered by the headlight switch anymore? Second question. Anyone experienced loss of headlights as a result of adding LED Tail lights , parking lights and the appropriate LED turn signal flasher.

02-22-2020, 03:07 PM	#2
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,563	Re: Headlight in 69 C10 quit working The whole system works on 12v, so you should have 12v at the switch. With engine running it could be more, such as 14V. Most likely problems in a headlight not working situation are bad relays, bad hi/low beam switch, and burned out headlight bulbs, and burned out fuse (if the relay harness has a fuse). Are both high beam and low beam not working? I recommend using a probe type test light or multimeter to check if you're getting voltage at the relay, and voltage at the headlight. You can use an alligator clip test wire to bypass your wiring and check if the headlight bulb works. If you have the type of relay harness that plugs into the factory harness at the headlight connector, you could just unplug the relay harness and plug the factory headlight connector into the headlight and see what you get. I don't think it is likely LED tail lights, parking lights, and flasher module would affect headlights.

02-22-2020, 10:59 PM	#3
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,936	Re: Headlight in 69 C10 quit working Check the dimmer switch first thing. Take the wire connector loose and see if you have power on it. Dimmer switches are know for headlights to not work. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

02-23-2020, 08:29 PM	#4
franken Registered User Join Date: Jun 2013 Location: Somewhere Posts: 3,053	Re: Headlight in 69 C10 quit working Yes, dirty contacts on the dimmer can cause this. Cycle the dimmer switch a bunch of times. It's worth a try and free.

02-23-2020, 10:32 PM	#5
Rick Bollinger Registered User Join Date: Mar 2018 Location: Colchester IL Posts: 282	Re: Headlight in 69 C10 quit working After dimmer check your grounds directly at the headlights



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