e450 grand touring series lexington

Hello everyone I ma new to the forum and have a big problem I need assistance with. I work at a Ford dealership and we had a 2004 e450 Lexington towed in. the customer hooked up the house batteries backwards. He then started the vehicle it ran for 5min or so then died now the vehicle cranks but wont start. I have no rear lights like stop/turn and when you but your foot on the brake I loss communication to instrument cluster (IC)when you but hazards on same thing and when you turn head lights on I loss communication until I turn them off then while cranking the IC will blank out and only leave battery light on. I have check all fuses and wire check connectors and pulled them apart to look for anything melted. the camper did not blow any fuses unless im missing one. this is not my vehicle and we do not work on campers unless it is for state inspection. has anyone else done something like this? I just want to cover all my bases befor I say it needs a PCM and an IC. I did contact the company that made this unit with no luck or help I need a camper wiring diagram. thanks