780 frame ground

I don't think you can really miss it? Check the insides of the frame rails close to the batteries?

 

Every single truck I've ever owned, from that first 500 dollar pos '73 cabover freightliner to my worn out '91 379, to this Columbia I bought new in 03, the main frame ground came off the starter.

 

I second the starter comment

 

The newer trucks do not run a wire from the starter to the ground. Look at the neg battery post and follow it to were it bolts to the frame. Then look to see were the ground goes from the front of the starter. Most of the time its above the front axle.