headlights not working

[dzbowtie]

Hey guys, went out this morning and headlights would not turn on. All marker and brake lights work. The dome light works when tried also. Could this be a switch if all other lights work? Just happened out of nowhere. My headlights also have aftermarket relays. Thanks in advance.

[cdowns]

check the dimmer switch and see if there is power there

[_Ogre]

no idea what year truck you have...
read this thread it has a lot of info on the headlight circuit
tail, brake, marker and dome lights have little in common other than the switch, different circuits all together
do your instrument panel lights work?

though i suspect your headlight relays are the culprit and since it's custom no one can throw a wiring diagram up and say ''here''
i am not a fan of relays in the low beam headlight circuit, it adds multiple failure points in a critical circuit
high beams circuit? ok. you can always switch to low beams

if you own and can use a multimeter, start chasing the power

and read my signature line, the lower one that says... how to put your truck year and build thread into your signature

[dzbowtie]

Its a 70 c10. All dash lights work, dome, marker, tail, etc. Just no headlights. Ill check the dimmer switch and start chasing power.

[dzbowtie]

I unplugged the wires from the relays and connected them. I checked the male/female connections to the original wiring to the relay wiring. I'm not sure the issue but I pulled the headlight switch and the lights came on. Could there be an issue or any way to test the mounted relays themselves? They are the black relays that come with the LMC kit.

[VetteVet]

You can test the relays easily without using the headlight switch or the dimmer switch.
You will have to determine whether the 85 terminals are the grounds for the relays or if the 86 terminals are used as the grounds as in this diagram. You also need to make sure that the grounds are good.

Once you have done that, just jump between the no. 30 terminal and the 85 or 86 whichever is grounded and the relay should close and the headlights should come on for low or high beams depending on which relay you are jumping.

If the relay doesn't close, check for power on the red wire from the battery.

If the relay closes with the jumper but not with the dimmer switch, then check the green or tan wire connections at the dimmer switch and at the relays.

[_Ogre]

Originally Posted by VetteVet

Once you have done that, just jump between the no. 30 terminal and the 85 or 86 whichever is grounded and the relay should close and the headlights should come on for low or high beams depending on which relay you are jumping.

i believe vetvette meant whichever is ungrounded (85 in his diagram), using the grounded side will blow the fuse in the red wire

as vetvette mentioned, check power at the red wire
if you have a fuse where he has fuse/breaker indicated; it should be an auto reset breaker for this exact reason
you do not want a headlight fuse popping, an auto reset breaker will flash and allow you to safely pull over

[VetteVet]

Originally Posted by _Ogre

i believe vetvette meant whichever is ungrounded (85 in his diagram), using the grounded side will blow the fuse in the red wire

as vetvette mentioned, check power at the red wire
if you have a fuse where he has fuse/breaker indicated; it should be an auto reset breaker for this exact reason
you do not want a headlight fuse popping, an auto reset breaker will flash and allow you to safely pull over

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Yes you are absolutely right. Thanks for the correction I was getting ready to leave for that big turkey dinner and in a bit of a hurry. I try not to make goof-ups like that but I'm sure glad you guys keep me straight.