Last weekend following a successful but wet July 4th camping trip, I hooked up my 5th wheel to the TV. Completed all items on my checklist. Started driving out of the park. About 1/4 mile outside the park gate, I get a "Fault Wiring" indication with the trailer (Ford F-350 data display). I am in a tight spot on a country back road and can not pull over immediately, so I drive on for about another 1/4 to 1/2 mile. Find a little grass shoulder to pull onto, I stop. I now also have a "Trailer Disconnected" warning in the data display. Upon getting out of the truck, I see that my trailer wheels/brakes are smoking (no fire, just light smoke). I too checked the TV to Trailer umbilical - it appeared to check good but the "Trailer Disconnected" text is still showing. (wished I had a 7 Way Trailer Connector Vehicle Tester 7 Way Trailer Connector Vehicle Tester Tow Ready Wiring TR20117
I then proceeded to check every fuse (in the truck) associated with the trailer and brakes. All checked good.
A good samaritan camper stopped and crawled all around and underneath the truck and trailer. We scratched our heads and came to a guessing conclusion that the electrical brakes associated with the trailer had either siezed or inadvertently employed. I walked back to the truck hitch area and saw that the emergency brake lanyard was still hanging down (appeared connected) from the pin box, but when I grabbed the lanyard, the lanyard pin fell out. Aha. Because the pin was not completely seated properly, the system showed the Trailer to be disconnected. Once I firmly reseated the pin into its receptacle, the caution..."Trailer Disconnected" disappeared and was replaced with "Trailer Connected". Problem solved in my case. Needless to say, I have modified my checklist to now read Visually and physically check that Emergency Brake Pin/Lanyard are firmly seated and TV data screen states "Trailer Connected".
The only other clue to your specific problem mentioned in the original post is something my dealer told me when I picked up my RV. He stated that an under charged battery may not provide the correct voltage to get correct readings such as the Ford truck warnings. This has not proven to be the case in my situation. Good luck in troubleshooting.