crawl under the truck and find your 12v+ wire at the connector behind the drivers wheel well liner and follow it to the back feeling and visually checking every inch, may have to unwrap the harness. insulator has been compromised some where and wire has been turned to green dust. Had same thing happen to mine a couple times. Mine was above the fuel tank on the drivers side, hardest spot to get at I think. Also while your under there check your trailer brake wire too mine crapped out too, brake controller would show connected but when I applied brakes if would go out and no brakes.