I got a 2000 ford f350 7.3 diesel and the problem is the truck won't start, and the scantool shows the ecu isn't communicating but theres no codes for loss of communication so i checked fuses and relays and wiring all appeared good because i had continuity from all wires, from the obd2 port to the ecu so i thought bad ecu so i changed the ecu and i have the exact same results. Both the pcms, the (canbus -) is shorted to ground, at the obd2 port pin 2 and pin 10 are the canbus pins, with the ecu unplugged both pins are ol when checking for shorts but with the ecu plugged in doesn't matter which ecu is plugged in (have only 2) pin 2 becomes shorted to ground. Are both modules bad or could something else the ecu power be shorted to ground which is grounding the canbus wires.

How i checked for a ground was with a multimeter checked for ohms and one lead on pin 2/10 and pin 4. With pin 4 and pin 10 tested i got OL when means no short to ground and with pin 4 and 2 i got a ohm measurement (dont remember the exact measurement) but if i unplug the ecu pin 2 then shows ol.

For diagnosing, i unplugged 90% of the harnness, idm, abs, engine plug above valve cover, 4 plugs on a bracket im assuming is transmission plugs, only part left is the part that goes to the other side of the engine bay where the blower motor and vaccum pump are but i dont think anything over there goes to the pcm to cause a short. I have literally tried everything while unplugging stuff i did get communication and i plugged everything back in and i still had communication and randomly lost communication again and reunplugged everything and still have no communication, i have officially gave up