Originally Posted by DMT
The F150 fuse and relay noted are both for the circuit to supply high current to charge the trailer battery. Has nothing to do with the brake controller. I towed 2500 miles without the fuse/relay and had no problems or messages from the integrated brake controller. Suggest you focus on trailer shorts or dirty connection at the plug. The suggestion to swap trailers or tow vehicles is good and may determine where to point the finger.
they are for powering the charging circuit to the trailer batteries only.
some say to leave out when not needed-- as if left in the 7way connecter has 12+volts that are not being used, but can cause the 7way to corrode with moisture.