mine did the same thing it would say trailer fault whenever you hit the brakes and sometimes trailer disconnect but the lights would work fine and this was on a brand new trailer so I hooked a buddy of mine trailer up to it and it worked perfect so I traced my brake wires from the tongue back to the axles and found out that one of the wires had been pinched in half and the other was smashed inbetween the trailer floor and the side frame after I spliced the wires back together everything worked perfect.