2017 New truck says 5th wheel it not connect? Update 2-14-18

I had a similar problem, at least the part about saying the trailer wasn’t connected. I first tried making a better ground connection and that worked for awhile. Ended up changing out the whole 7pin female plug assembly on the truck. That was 2 years ago and I haven’t had any problems since.

Usually the fast flashing on the turn signal is a sign of a too small flasher. Hard to believe that would be an issue on a new F350 though.