87 Ford E350 Signal light Problem

Many years ago with our first motor home on a Toyota chassis, 10 or so years into ownership, we developed an issue with the tail lights. They simply stopped working. After going through everything, I concluded there was some kind of problem with the wiring between the front and back of the rig. It didn't take long for me to discover that the outfitter had cut the wire harness by the passenger door threshold with a utility knife when trimming the RV carpeting inside the cab. All but a strand or two were cut and after 10 years, the remainder eventually burned away like a fuse.

Something to keep in mind, the harness might be damaged somewhere inside the cab area by either the outfitter or previous owner.