98 Peterbilt model 378 Left turn signal problem while clearance lights on

Those are tough! TA/petro is pretty good at finding electrical issues

 

They spent an hour chasing an issue for me once. They were about to give up. Then I turned the switch on for them. You have to watch those guys sometime

 

I don’t doubt it one bit! I’ve had good luck in OKC, Joplin, and York Ne. But yes there’s always some questionable ones.

 

If it does it with pigtail unpluged from under truck, replace bulbs on side of tractor then replace ft. bulb? One of them is shorted out the cost of bulbs is nothing when compair to 1 hr of labor at shop?

 

Are all stop, tail and turn signal lights working with the lights off? If I have a turn signal out on the back of the truck I have the exact same problem. I use incandescent lights on the rear of the truck and LED everywhere else. The incandescent lights burn out fast and I can always tell when the do because the turn signals act goofy. Electricity will follow the path of least resistance and do strange things when the normal path is interrupted

 

I’m going to guess bad ground at the trucks taillights.