I found a similar problem with my older F-250. The controller would display "NC" when connected to the trailer. All wires appeared sound.
What I found was that a rock had impacted the 7 pin wiring connector on the truck and parted a wire within its sheath. This was unobservable by looking at the wire bundle. Try the lowest wire going into your connector, wiggle it and push it about to see if you have lost the copper connection within the wire. If you have an assistant, monitor the controller messaging. If you can wiggle out a good connection, the monitor display will change to "connected" or a voltage value.