I'd check the back harness and work your way back. The Starcool shore power compressor is mounted outside on the frame on most builds. Pretty sure the lights run inside the body...I could be wrong but I lost my backups and had to bypass the wiring behind my cabinets and install a new run along the frame. Maybe take a look at any fuse taps that SMB might have tampered with under the dash. Might be an easy fix.
2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer