I WAS DRIVING MY LEASED, 2003 VOLKSWAGEN JETTA, (EQUIPPED WITH COLD WEATHER PACKAGE), ON A VERY BUSY ROAD IN LATE AFTERNOON ON A COLD AUTUMN DAY JUST OUTSIDE OF BOSTON. I TURNED MY DRIVER SIDE SEAT WARMER ON THE HIGHEST LEVEL, (5) AND IN ABOUT 5 MINUTES I FELT A SHARP PAIN ON THE BACKSIDE OF MY LEFT THIGH AND THOUGHT SOMETHING HAD STUNG ME AT FIRST. I REPOSITIONED MYSELF IN THE SEAT, AND COULD SMELL SOMETHING BURNING. I LOOKED DOWN AND SAW DARK BROWN SMOKE POURING FROM THE SEAT AND REALIZED THE SEAT WAS ACTUALLY BURNING ME. I IMMEDIATELY TURNED THE SEAT WARMER OFF, PULLED OVER, (AGAIN IN VERY BUSY TRAFFIC IN WATERTOWN, MA), AND GOT OUT OF THE CAR TO FIND A DARK BROWN, DIME-SIZED BURN MARK IN THE SEAT!!! THE HEAT ACTUALLY WENT THROUGH THE SEAT AND BURNED A SMALL BROWN MARK INTO MY BLUE JEANS AND SUBSEQUENTLY, LEFT A SMALL WELT ON THE BACKSIDE OF MY THIGH. I AM SCARED TO DRIVE THE CAR NOW BECAUSE I AM NOT SURE IF THERE ARE OTHER ELECTRICAL DEFECTS WITH THIS CAR THAT MAY PUT MY LIFE, AND MY PASSENGERS LIVES IN DANGER. I HAVE CONTACTED THE DEALERSHIP I LEASED THE CAR FROM AND THEY SEEM VERY EAGER TO REPLACE THE SEAT AND TO CLEAR THIS MATTER UP IMMEDIATELY.