PASSENGER SEAT MOTOR OVERHEATED. INITIAL INDICATION WAS SMELL. SEAT IS POWERED (FORWARD AND BACK ONLY). SEAT SWITCHES WERE NOT IN USE AT THE TIME. VEHICLE WAS IN POWERED AND IN MOTION. SMOKE FOLLOWED W/I 20" OF INITIAL SMELL. VEHICLE STOPPED AT SIGHT OF SMOKE AND DRIVER WAS ABLE TO LOCATE PLUGS FOR MOTOR UNDER PASSENGER SEAT. DRIVER REMOVED PLUG, BURNED HAND SIGNIFICANTLY IN THE PROCESS.