PASSENGER SIDE FRONT SEAT CAUGHT ON FIRE FROM THE SEAT HEATER. KEPT SMELL A BURNING SMELL AND COULD NOT DETERMINE THE SOURCE. PARKED THE TRUCK AND LOOKED OUTS DE ABOUT AN HOUR LATER. SMOKE COMING OUT OF THE CAB. OPENED THE DOOR AND SAW SEAT ON FIRE. YOU ASSENGER USED THE SEAT HEATER PRIOR. NO ONE SMOKES IN MY FAMILY SO THERE WAS NO OTHER HEAT SOURCE.