WHILE DRIVING, HEAVY SMOKE CAME FROM DASH. I PULLED OFF TO THE SIDE OF THE ROAD. WHEN I LOOKED UNDER THE DASH I COULD SEE WIRES MELTED TOGETHER COMING FROM THE BRAKE LIGHT SENDING UNIT. IT MELTED UP INTO THE MAIN WIRE HARNESS. I UNPLUGGED THE WIRES , BURNING MY HAND. IF I WOULD NOT OF, I BELIEVE THE TRUCK WOULD HAVE CAUGHT ON FIRE!*AK