REAR DEFROSTER SHORTED OUT. OVERHEATED AND CAUGHT THE PLASTICS ON FIRE. THE WINDOW THEN SHATTERED FROM THE EXCESS HEAT FROM THE REAR DEFROST. THE VEHICLE WAS IN MOTION ON THE HIGHWAY. OUTSIDE TEMP WAS 28 DEGREES. REAR DEFROST AND HEAT WERE ON FOR THE VEHICLE. WHILE TRAVELING, THE VEHICLE BEGAN TO SMOKE INTERNALLY. THE CAR WAS PULLED OVER, AND SHUT OFF. THE SMOKE STOPPED AND THE WINDOW SHATTERED. THE PLASTIC AND SEAT SURROUNDING THE REAR DEFROST CONNECTION TO THE WINDOW WERE MELTED.