High Beam issue

[mikey531]

I went on vacation for 2 weeks and left my 1969 GMC C-1500 truck sitting in my garage. I went to open the hood and it was hard and wouldn't stay up, one of the lift cylinders on my billet hinges stopped working. Ok I called and have two new ones coming. Then yesterday I was checking my lights and turned on the headlights low bean and lights all worked hit the dimmer switch for high beam and low beam went out and the high beam didn't come on ! I bought a new dimmer switch no change. I have been chasing wires from the bulkhead to everywhere they are supposed to be. Nothing. The light switch was new 5 years ago and everything worked 2 weeks ago !!! Where do I go next? I think my truck may be mad at me.

[RustyPile]

First step is to round up three important tools (1)test light or volt meter, (2) wiring diagram, (3) A well-fitting "do not assume" hat.. Guessing and throwing parts, and hoping something sticks is not a proper repair method..

Voltage comes from the headlight switch to the dimmer switch through the light blue wire.. Since you have low beams, that circuit is working.. At he dimmer switch, you should have voltage alternating as you "flip" the dimmer switch, on the light green and tan wires. If you don't, the switch is bad.. If you have voltage on both wires, check for continuity on both these wires at the firewall connector, Again, alternating on each of these wires on both sides of this connector. If voltage is present on both wires on both sides of the connector, continue checking the wires inside the harness for breaks.. Check for voltage on these wires at the plug at the headlight bulbs...

[mikey531]

Did all that I am getting a new relay later this afternoon.

[54blackhornet]

Wiggle the plug at the bulbs.

[mikey531]

did that it was all new American wire when I built it. It was working fine when I parked it two weeks ago.

[Stocker]

Originally Posted by mikey531

Did all that I am getting a new relay later this afternoon.

I must have missed something, didn't think these trucks had headlamp relays. If relays were added (great idea, btw) then yeah, that could be the culprit.
I would troubleshoot with a VOM or at least a test light before throwing a new relay at it, though.

[Palf70Step]

Last 4-eyed truck I had had same issue, turns out both hi-beam bulbs were dead.

[mikey531]

Originally Posted by Palf70Step

Last 4-eyed truck I had had same issue, turns out both hi-beam bulbs were dead.

Already checked them and they work

[Wrenchbender Ret]

Check the plug at the dimmer switch. It is well known to get corroded. It is in a poor environment

George.

[franken]

Cycle the dimmer switch 20 times.

['68OrangeSunshine]

Are Rodents a possibility?
Here in the South West, Packrats will invade an engine bay in no time. They chew thru wires. A couple of months ago, one chewed thru #5 spark plug wire on the 350 in my '71 GMC Jimmy. I had started the Jimmy to move it out from under a canopy so I could work on my '03 Tahoe in the shade. The Jimmy started OK, but sounded rough. While working on the Tahoe, I dropped something small and searched under the engine. I didn't find what I wanted, but I did find a 1'' piece of blue 8mm plug wire. So I looked under the GMC's hood. Sure enough, the little SOB had attacked my plug wires. I put on another plug wire from a different set and it fired OK. But I was mad a nice Blue 8mm Taylor wire set was compromised.
One local trick is to leave the hood up. Packrats won't nest where a cat can get at them.

[mikey531]

Thanks for all the help, I found the problem.

[RustyPile]

Looks like moisture got to it.. I hear it's a common problem with the relays in those headlight kits..