1986 C10 Headlight Issues

[CATXTraveler]

Hi all,
Thought my headlight issue was resolved.

Currently, I have no headlights.

I have 12v going into the dimmer switch from the big red wire.
Something strange is I either have 12v or about 3v coming out to the yellow wire which feeds the H/L switch.
Regardless however, 12 or 3v, I have no lights.
I then jumped the yellow wire going into the H/L switch to the green wire on the H/L switch after replacing the switch and no difference was made and the headlights still don't turn on.

Any ideas? I'm pretty stumped. Should I try jumping straight from the red wire on the dimmer switch to the green wire on the H/L switch to see if the headlights will turn on? They will turn on if I connect 12v from the battery directly to the green or tan wire at the headlight itself.
What's causing the voltage drop through the dimmer switch?

 

[CATXTraveler]

I have also tried the following:

1- connect jumper wire to green wire from H/L switch (this wire I believe goes out to the headlamps)
2- Insert multimeter and connect to yellow wire coming from dimmer switch (12v power source to H/L switch)
Multi-meter will be showing 12v.
Once I jump the green wire directly to the yellow wire (which is what would happen inside the H/L switch, correct?)
It kills the power-- multimeter doesn't register any voltage. I would imagine that this would instead trigger the headlights to come on.

 

[CATXTraveler]

Update for anyone following along or that might have this same issue down the road.


I used a power probe.

I’m getting 12 to H/L switch
If I send 12v from the H/L switch pigtail it will turn on either high or low beams depending on which color wire.

The kicker though- my power probe is telling me that without 12v applied, both the green and tan wire are connected to ground. Is this accurate? Or is this reflecting a short-to-ground? If it's a short- I'm surprised that it's both wires. Any ideas on where to start looking?

 

[CATXTraveler]

This is starting to feel like a personal diary of someone right before they burn their truck down.

I disconnected the plug from the firewall so I could test if the ground was in cab or engine bay.
I probed both tan and green headlight wires and they still showed they were grounding somewhere. At least I know the issue is now somewhere in the engine bay.
Time to tear apart the front end and pull apart the wiring loom.

Hope this is the right direction.

 

[Scott91370]

I'm probably not any help here buyt when you say H/L do you mean:
1) Headlight (dash switch)
2) Hi/Low (column switch)

 

[Matt69olds]

I assume you mean you have power on the large red wire at the headlight switch?

If you study the diagram, power comes in on the large red wire. With the park lamps on, you should have power at the brown wire (parking lamp feed) the green wire is dash lamp power, it goes to the dash lamp fuse and comes out as a gray wire. In this diagram, headlight power is blue, on a squarebody truck of your vintage im almost positive it’s a yellow wire. It comes out of the dimmer switch as either tan or light green. White is courtesy lamp ground.

For testing purposes, take a FUSED jumper wire (10 amps would be enough I would think) and jumper the red to yellow wire. See if the headlights work. If so, replace the headlight switch. If not, jumper the red wire to either the tan or green wire at the dimmer switch. Either the high or low beams should light.