If, after they repack your bearings and check your brake magnets/wiring, you still have the fault light. go to a trailer supply store and buy a replacement trailer connector. BARGMANN brand is what's on the Ford truck and if you replace the trailer end with a Bargmann, I'd almost guarantee that you won't have any more problems.
Here's one of many discussions from "years gone by":
http://www.keystoneforums.com/forums...ight=umbilical