WHILE IN CRUISE FLIGHT A FIRE ERUPTED BENEATH THE CABIN FLOOR DIRECTLY BENEATH THE RIGHT FRONT SEAT. UPON LANDING THE FIRE WAS EXTINGUISHED WITH THE AIRPLANE'S FIRE EXTINGUISHER. EXAMINATION OF THE AIRPLANE SHOWED THAT AN ELECTRICAL WIRE HAD BEEN TIE WRAPPED TO A FUEL LINE. THE INSULATION ON THE WIRE HAD CHAFFED THROUGH AND THERE WAS A HOLE IN THE FUEL LINE. IT COULD NOT BE DETERMINED WHO PERFORMED ANY WORK IN THAT AREA.