Headlight issue - Pete 589

That's funny he didn't repair but tell you how to make it work. I would of made him sign the DVIR that he certifies it's safe to operate.

Peterbilt's headlight circuit is fairly simple compared to some trucks. You have two relays a low and high beam. If one of them was bad both lights would be out.

The ground wire is shared. It runs to the right headlight and is pigtailed over to the left head light. Follow that black wire and you should find it splitting off near the right headlight.

My guess is that ground pigtail has a poor connection and I'll tell you why I think that. You said it works with the truck off. When you flash high beams or start the truck you create a power surge just enough to rob what little ground connection is left to that headlight.

When you have the light on in the broke mode play and jiggle that pigtail split around. Sometimes it's just easier to run a new chassis ground to the left side and let each side have it's own dedicated ground. You could temporarily take a 3-4' piece of jumper wire, hold it on the left side headlight ground and the other end to chassis ground. If I'm right the light will come on.

That should be a warranty repair. People like us do what we can to make it work. A trained Peterbilt mechanic should be fixing it right instead of coming up with some lame idea. That would include a new harness.

If it doesn't meet your satisfaction write it up again.

 

Been having this same problem with my rightside. I replaced the headlight socket because I noticed a burnt/scorched mark where the ground connection for the bulb meets in side the plug. After 2 months now I'm getting the same thing. Must be a bad ground.