1997 Peterbilt 378 Crank no start

Electric welding maybe? That current wants off that frame somewhere and it's going to find it's out when it wants out. Usually burned something on the way out.

Your sequence of problems leading to a dead engine tells me maybe in your harness and or fuses you might have lost several wires or pathways between you and the ECM. Take a look at your fuses see how they are doing.

That would be where i start.

 

Did you see them take the batt. cable off before they started welding, you will have to find the fuse in the batt. box that powers the ECM its in a small box like a ad on type fuse ck all batt conn. for the small POS. and NEG, wires that lead to the fuse that powers ecm follow them to the panel in dash then ck key switch for power till you find where power stops

 

I had a 5ek that wouldn't start , come to find out it was the cam sensor that was located on the side of the cam gear , it was removed and the green piece at the end was pulled out some , reinstalled and truck started right up , still running today