Ford has had an issue with the wiring harness somewhere between the front of the truck and the trailer plug. On my 2002 F350, I had to abandon the wire in the harness and wire the trailer clearance lights into the tail light circuit on the truck. Never had anymore issues.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot