I REMOTE STARTED THE VEHICLE FOR ABOUT FIVE MINUTES. I THEN GOT IN, AND TURNED THE KEY ON AND SAT IN THE VEHICLE. WHILE IT WAS IDLING, I SMELLED SOMETHING BURNING. I OBSERVED A RELAY? ON THE REAR WINDOW BURNING. I COULD SEE A FLAME (INSIDE OF THE TRUCK) , AND THE TRUCK CAB FILLED WITH SMOKE. THE RELAY EXPLODED, AND THE REAR WINDOW SHATTERED. I SHUT THE TRUCK OFF, AND THE FIRE WENT OUT. I OPENED ALL THE DOORS AND CLEARED THE SMOKE OUT. I BELIEVE THE RELAY FOR THE REAR WINDOW DEFOGGER FAILED, CAUSING IT TO OVERHEAT AND START A FIRE. I AM REPLACING THE ENTIRE REAR WINDOW. THIS IS A FIRE HAZZARD, AND A DRIVING HAZZARD DUE TO THE CAB FILLING WITH SMOKE. THERE WAS ABSOLUTELY NO WARNING OR WARNIG LIGHTS THAT THIS WAS ABOUT TO HAPPEN.