I TURNED ON REAR DEFROST AND WITHIN FEW SECONDS BACK SEAT WAS ON FIRE. WINDOW BURNT SEAT AND SEAT BELT ALSO BURNED HAND. IT APPEARS TO HAVE BEEN A POSSIBLE ELECTRICAL CAUSE. I FIGURED A FUSE WOULD BLOW PRIOR TO A FIRE INSIDE CAR. HAD I BEEN ON FWY I WOULD HAVE NOT BEEN LUCKY GAS TANK IS INCHES BELOW FIRE .