I had a similar issue with my Ford truck---intermittent brake connection and finally, no connection at all. I actually bought a new controller, hoping to fix the issue. The problem was not cured.
The cause was the wiring to the truck's 7 pin socket. The brake wiring from the truck enters the socket at the lowest point to the pavement. Evidently, a rock or other road debris had hit the brake wire and damaged it. The wire jacket was still intact but the inner threads had parted.
Cure was to remove the trailer umbilical socket on the truck, disassemble it, strip truck's brake wiring to good wire, reattach to socket, and reassemble socket. It sounds easy but there are a lot of small pieces involved. If you're not conversant with electrical harnesses, I'd seek help if this is your issue.
Diagnostics can be performed for a problem like this by activating the brake controller (or have an assistant monitor for connection if your controller displays a "NC" condition), grasping the brake wire close to the socket, and moving it while monitoring. If unhooked from trailer, observation of voltage at the trailer brake output pin would work as well if doing the above procedure.
Good luck with the brakes issue, hopefully it is just a tarnished socket pin.
