Truck Repair Electrical Help


New Member
I have a 98 Peterbilt 357 that I’m having trouble with . My problem is when my running lights and headlights are on my battery reads about 10 volts. The batteries are less than 5 months old and we just put in a new alternator, also when my lights are on my turn signals only want to blink like once or twice then they stop. The driver side marker/signal stays fully lit when the lights are on. seems like it has a bad ground but I cannot seem to find it though. Everything works fine when the headlights and running lights are off. The lights are all Led


Friendly Neighborhood Former Technician
I would start with battery to frame ground clean the connection spots and make sure it’s tight. Also. If you have like a Delco 24SI or 31SI alternator make sure you have a good excite wire on it that reads true battery voltage. The other thing is there could be corrosion inside the wire insulation on your pos or neg battery cables, and or your alternator cable. I would look at those closely as well. Road chemicals from winter in a pin hole in the insulationcan kill the whole truck.


curmudgeon extraordinare
Start pulling fuses and seeing if anything changes.

If that doesn't work, start pulling light bulbs.


Staff member
when dealing with electrical issues the first thing to think about is grounds,grounds, and grounds 80% of the issues will be poor grounding


Professional Pot-Stirrer
The driver side marker/signal stays fully lit when the lights are on.
So when your lights are on, thus one stays at normal brightness, and the others - head lights, etc - are dimmer?

If I'm reading this right, after looking at the above, if there's still trouble, I'd find out why this one isn't behaving like the others. That may be where your trouble lies.