2003 peterbilt 379 Burned wire smell.

Are your batteries getting overcharged. That would be a rotten egg smell.

 

I usually smell that when (exposed) wires touch or a small motor burns up. It's a very distinct scent.
In any case, the alternator could produce that scent. Also, perhaps consider checking the belts.
What's happening when it happens? Is the fan running? AC on? Pressing brakes? Pressing clutch? Any popped fuses? Hitting bumps? Etc.

Also, not to be funny, but if there's truly no identifiable cause, it could just be a "phantom scent" caused by an olfactory (sense of smell) disorder called phantosmia. Phantosmia can be caused by allergies, colds, sinus infection, dental issues, etc.

In any case, I hope you find it before it finds you!

Good luck to ya,
Cheers!

 

Could be the a/c blower motor getting close to going out. I’ve smelled that before sometimes weeks or months before one quits. That thing usually runs as much as the big horse does.

I’ve also noticed really funky smells associated with the new pelosi diesel fuel we are forced to run. I get weird burning plastic smells and sour gear oil smells from time to time and it’s not just coming from one truck. Lol.

 

No worries, you're welcome! Glad you found it and I always appreciate the update! You actually got back pretty quick! Just happy to hear the riddle is solved!

Kind regards,
5UG