2006 Peterbilt 379 Blowing fuses for high beam headlight. (2024)

My 2006 379 peterbilt is blowing the high beam headlight and headlight fuse. Turn on headlight switch and marker switch. When I turn them off, the marker lights stay on and the switch stays green even though it is off. If I pull the marker relay or hit the courtesy flash switch, the markers turn off. It even blows the high beam headlight and headlight fuses sometimes. Sometimes it will not blow the fuses for a few days and sometimes it will blow them as soon as I turn either switch on. Almost like the marker function on both switches are bumping into each other and blowing the fuses. I am thinking the relay for the markers is sticking on. I am going to replace all relays tomorrow and pray that fixes it. Anybody have a good answer for what is happening, I am open to that just incase the relays do not fix the issue. I did replace both headlights and almost all the wiring in the front as well as the rear after the issue started. It still does the same thing. I violently shaked all the wiring in the dash and everywhere I can to try and blow the fuse but they will not blow and all the sudden Im sitting there and they just decide to blow.

Yep, it's a 379 Pete alright. Years ago, we'd wrap the fuse in aluminum foil and see where she starts smoking. Trucks were a lot tougher then. I don't recommend that today. 379's are notorious for fuse box problems. 1st thing I'd do, is make sure the cab has a good ground to the frame, run another, if need be, and go from there. Hard to say what's causing it, as electrical does funky things and can back up through other things. I bet the problem is behind the fuse box. Good luck.

Thanks. I removed the fuse panel and seen no issues at all. Very little corrosion that I cleaned out and recrimped all the wire ends and replaced all fuses. Still an issue. I just now replaced all relays and that did nothing to resolve the problem. Guess I will go back out there and keep searching and also make sure the cab is grounded.

Check the wires going to the headlights in the area where the hood is hinged.

I just now, after 3 weeks of dealing with this, found the problem.
In the past, the original stock power wire to turn the marker lights on went bad so somebody ran a new wire and did not cut the stock wire out. After time the stock wire decided to work again si it was clashing with the replacement wire and pulling it into the same problem the original wire had. I completely removed the stock wire and ran a new thicker gauge wire and the lights work great. No more issues. Thank God!!

I thought I had it fixed but it did it again. Blew the marker and headlight fuse. It stays on when stationary but as soon as I move the truck it blows the fuses. Not sure what to do anymore.

Ain't trucking fun? Since you say it only happens when you move, I'd check the brake lights. If you don't have LED's, it could be something as simple as a filament touching or whatever turns the lights on when the parking brake is applied. Just think, you could be paying someone $150/hr. to come up with nothing,,,

Have you checked resistance thru both the dash switch and the flash to pass switch and the wires connecting them. Look for “welding” at connections or visual giveaways of #### getting hot. And I would clean every ground you can chase down and that is just good practice to keep them clean makes a hell of a difference in the headlight and marker lights brightness.

I love those old Pete’s though.

I'm with IH guy, I think you should check the wiring at the hood hinge. The 14 I drove had a similar issue. It couldn't hurt to check your bulbed lamps like the one dude suggested.