Headlight wiring help

[fpchief]

I bought this truck as a parts truck and it has ended up being something I will not be parting out. It had a corroded wire #10, from magnetic relay that I had to repair to get it started. Figured I would eventually have more wiring issues. It sat down near the beach for a long time.

Replaced each connector on starboard headlight, replaced the high beam switch (used from another member, replaced because the first time I hit it for high beams it made all the lights go out)

Now, turn lights on and nothing. Hit high beam switch and only port side light works. I am getting no voltage (nothing above 2.5vdc) ar no connector. I am pulling plug off back of bucket and touching positive inside plug and got fluke ground going to chassis.

Is there a common place in the harness that may corrode and be hidden?

 

[Mullaney]

Sounds like a stupid idea until you think it through -- but when I try to chase down a wiring problem I go directly to the negative post on the battery. I have a big fat alligator clip on one end of a piece of 14 gauge wire. I stick it up on top of the battery terminal where a good hard yank will pull it free. The clamp on the other end of the tester onto bare wire is the second fail-safe. And while I am hooking up to the negative battery terminal - I double check that my test light works on the positive battery terminal.

Again, seems kinda redundant, but these trucks appear to have a REAL PROBLEM with good grounding 30 or so years after they were manufactured (and left sitting alone in a boneyard for ## years - baking in the sun).

You definitely need to confirm a "no questions / no excuses" good ground to test with.

Especially on a headlight. On a fender that should be but might not be grounded...

 

[fpchief]

Sounds like a stupid idea until you think it through -- but when I try to chase down a wiring problem I go directly to the negative post on the battery. I have a big fat alligator clip on one end of a piece of 14 gauge wire. I stick it up on top of the battery terminal where a good hard yank will pull it free. The clamp on the other end of the tester onto bare wire is the second fail-safe. And while I am hooking up to the negative battery terminal - I double check that my test light works on the positive battery terminal.

Again, seems kinda redundant, but these trucks appear to have a REAL PROBLEM with good grounding 30 or so years after they were manufactured (and left sitting alone in a boneyard for ## years - baking in the sun).

You definitely need to confirm a "no questions / no excuses" good ground to test with.

Especially on a headlight. On a fender that should be but might not be grounded...

I will be doing that.....thanks for the advice. If I can 100% be certain of the yes/no of voltage at each light connector I can go from there for sure.

 

[fpchief]

Using a ground going to battery, I have -12vdc on both power leads at each headlight and when I go to high beam I have +12vdc to #17 leads..both sides. Surely -12vdc is not correct. And with the +12vdc the high beams do work.

 

[cattlerepairman]

No, 12V is not correct. You should see 21-24V there......UNLESS perhaps you put your (-) on the "wrong" battery terminal and only have one battery in play? I would double check with a different ground.
If you have regular 24V headlights (incandescent or halogen) they would not light up well on 12V. If they do, you most likely have the correct voltage.

 

[fpchief]

They are dim when on high beam. First thing I thought is I had the leads backwards but definitely did not. I knew I would have wiring trouble on this truck eventually...so here it is.

Luckily, all the rest of lights work just fine, cranks good, etc etc. Just no dang headlights.