not that this was on a SD but on my F150 i had a heck of a time getting the trailer lights to work...checked all fuses, checked all relays, checked all the wiring (both truck and trailer), bought a new tow package harness...still no lights...well come to find out it was a bad fuse in a fuse box that neither the haynes or owners manual listed as being there. so i guess what i'm trying to say is it sounds kinda like a bad fuse and i'd start looking for boxes that shouldn't be there
