hp8850

Dean, you've troubleshot this issue to about the 90% level. Assuming you have the a chassis wiring diagram to your coach, you should be able to finish this off. As I understand it you do not see a short to ground at the engine end of the bus, but do at the instrument panel end. As you've noted, the next steps require you to go through isolating each of the segments to find what/where the short is. That is what a service center is going to do. They will be first charging you for validating what you've already discovered, and then going through the module discovery process, and then disconnecting each module from each segment, in the isolation process, all the while charging you by the hour. The problem is likely a chafed cable, in the harness. The J-1939 wires are buried in the wiring harness and are a twisted pair. There may be more than 1 set of twisted pair wires in the harness, one set for each wiring buses.