I have a 2008 f350, once and a while I will get a message on the dash display that will say "trailer wiring fault". It will do this whether Im hooked to a trailer or not. If I hook it to a trailer all the lights and brakes work fine. I do notice that when hitting the brakes when hooked to a trailer it doesnt show any brake gain on the display on the dash, it always shows "0" but the brakes work. Ive checked the plug and everything seems to look fine. Any ideas, thanks.
There was a post on the trailer lights that I read yesterday that is somewhat similar to this. I saw something like this a few weeks ago when I was towing my RV, I had trailer running lights but no brake lights or turn signals and no trailer gain. Found the trailer light fuse burnt out yesterday.
I had this happen to my truck . I took it to the dealer and they said water had gotten it to the hitch plug wiring and it will send a fault code.They blew out all the connection and just put some electrical grease on the connections . Have not had anymore problems since then and it has been about a year now. Hope this helps you guys.