Where to begin, The customer had a cat tech come out and check this truck out it just DIED then had Codes P03 P07 he hooked up his lap top couldn't hook up to the truck no communication with the truck so he tried a different computer still same thing so we got contacted to bring in and address the issue ( the customer wasn't very pleased with the CAT tech and his lack of answers ) So we bring it in with the original ecu pulled and the ecu he was trying to use hooked up. So I start checking connections at the fuse/relay panels (all 3) for blown fuses Corroded wires etc. Nothing call a cat dealer ask one of their techs what the problems could be he goes into how bad the wiring harnesses are in these P5000 Serial AT3512277 he tells me where to check for easy fixes nothing wrong. Tried to hook up OBD2 Scanner wouldn't even power up so starting to lean towards the wiring replace wiring harness from the factory the part number was 91a0459400 the build date of the truck is 1-21-08 so I pull the harness and install new. Cleaned all connectors of any corrosion the only place this was found was on the trans plug for power soft, the light plug and the ign switch plug. hook the wiring up double check all connections and pray..... Nope now I have P03 F04 tried the other ecu and as of today another ecu the same thing same codes could it be in the dash ? ive heard the vsm rarely goes out

ANY HELP would be appreciated thanks