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Discussion Starter · #1 · (Edited)
Hello. I recently purchased a 66 C10 with a 327 (2 speed auto), and I haven't been able to get the headlights to work. I've installed a new headlight relay, and new headlights (the old one's didn't have continuity), but they're still not working. Tail lights, running lights and blinkers work, just not the headlights. I've cleaned up all the grounds, but still nothing. The owner(s) before me kind of ""modified"" some of the wires, so I don't have any baseline information. I've looked online, but I'm still having trouble deciphering the diagrams. I've also ordered a repair manual a few days ago, but it won't be in till next week or so.

I've followed the red wire from the headlight relay switch through the fire wall, along the driver's side of the engine through the radiator. Looks like they're hooked up directly to the battery via butchered wiring.

I don't know anything about wiring, but I'm willing to attempt to rewire the headlights if I have to. But before I do, I wanted to ask others on the forum if I'm missing anything. I looked at the fuse box, but I don't see anything that is labeled for the headlights (and I'm not sure if they're supposed to be there anyways).

So, are the headlights supposed to be grounded individually to the frame? Are the headlights supposed to be hooked up to the fuse box? All lights are working except the headlights. I've been searching the forums and bing/google, but I'm still having trouble figuring out how to get these lights working. I appreciate ANY help. Thank you
 

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Yes the headlights are grounded thru the radiator support brace, on both sides, 99% of the problems do occur at the headlight dimmer switch on the floor left side, rust, moisture and dirt are the culprits. Sometimes its the firewall harness plug on the engine side just old and won`t make contact...its easier to replace, you can just buy the light harness thru LMC or Ecklers
 

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Discussion Starter · #3 ·
Thank you, 406Rich. I wasn't aware that the button on the floor was called a "dimmer switch" or that it would affect the headlights. I'll definitely check that out. If all else fails, i'll just replace the harness. Thank you again.
 

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Dimmer switch gives you your high beams vs low beam headlights, low beams for normal driving in city traffic, high beams for darkened country roads, they are notorious for headlight troubles from dirt and rust..
 

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Discussion Starter · #5 · (Edited)
After replacing the dimmer switch (and cleaning the terminals, which were beyond filthy), the headlights work. What a load off. On a side note, my passenger side running light stopped working, BUT it does flash when the turn indicator is activated. Since the running lights turn off anyways when the headlights are on, I don't think it's a big deal, just a minor annoyance. This should last me until I decide to buy a new harnesses.

Thanks again, 406Rich! Next up, getting the brake lights to come on when the pedal is pressed :) Time to go research.
 

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Brake lights check the plunger switch that resides under the dash at the steering column, activated by your brake pedal...ensure the wires are connected, if so squirt a little wd40 into it and work it a little and try it again..or it's a grounding issue, try a jumper wire from the tailight bucket to the frame for a better ground, these trucks are bad for grounds...In fact here is a to do upgrade for you sense these trucks are notorious for bad grounds, I`ve done the same..new grounds... engine to frame, frame to cab, cab back to engine, use 00 welding cable or the heaviest braided ground cables you can find, then new grounds for the tail lights from the twilight bucket to the frame... where ever you put a cable clean the paint and rust off use thru bolts with starr washers to bite into the steel...first thing you`ll notice is how much faster the engine will crank over and fire and how much brighter your head lights will be..and a host of other problems will go away or never happen...
 

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Discussion Starter · #7 ·
I'll definitely check the plunger switch and wires. This truck is in desperate need of an interior cleanse. I did not know that you can spray WD-40 onto connectors, but I'll give it a go. Putting in new grounds is something I'd really like to do. How long did it take you to finish grounding everything? I'm sure that's a whole lot of work, but worth the dependability.

Just for kicks, I attached a picture of the original dimmer switch in all it's filthy glory. Can't wait to get this truck cleaned. Been doing it slowly but surely.
 

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How long did it take you to finish grounding everything? I'm sure that's a whole lot of work, but worth the dependability.
Once you get the ground straps bought or made ( I made mine ) just an afternoon, If you look behind the right front wheel, there should be a very small ground strap done from the factory from the inner fender to the frame..that was the only ground strap the factory put on..all the rest of the grounding was relied on the bolts between body panels definitely not the best of systems.
 

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Discussion Starter · #9 · (Edited)
I installed a new stoplight switch. Both tails lights are on when the headlight switch is activated, but only one tail light lights up when the brake pedal is pressed. I guess for now one brake light is better than none.

To summarize, headlights work after new switch headlight switch and dimmer switch installed, but passenger side front running light doesn't come on, but it blinks when turn signal is activated. New stoplight switch installed, but driver side tail light doesn't come on when brake pedal pushed, but it blinks when turn signal is activated.

Thank you again for your help, Rich. You helped me a ton. I'll eventually just replace both harnesses or upgrade/redo the grounds.
 

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I installed a new stoplight switch. Both tails lights are on when the headlight switch is activated, but only one tail light lights up when the brake pedal is pressed. I guess for now one brake light is better than none.

To summarize, headlights work after new switch headlight switch and dimmer switch installed, but passenger side front running light doesn't come on, but it blinks when turn signal is activated. New stoplight switch installed, but driver side tail light doesn't come on when brake pedal pushed, but it blinks when turn signal is activated.

Thank you again for your help, Rich. You helped me a ton. I'll eventually just replace both harnesses or upgrade/redo the grounds.
Tailight and brake light bulb have two filaments in them, have you checked for a broken filament, also check the front bulb for the same or just not making contact, again just shoot little wd40 into the socket ( both non working lights) and see if that don`t work...glad its all working out for you...!
 
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