PICKED UP 1 YARD OF MULCH AND WAS UNLOADING, SMELLED BURNING RUBBER, AND SAW FLAMES IN WHEEL WELL. PUT OUT FIRE WITH FIRE EXTINGUISHER AND CALLED FIRE DEPARTMENT. OPENED HOOD, AND SAW FENDER BURNED, PLASTIC BRAKE NEAR MASTER CYLINDER BURNED, AND FUSE BOX AND WIRING BURNED. FIRE DEPARTMENT SAID IT WAS BAD WIRING. MECHANIC FELT IT INVOLVED THE BRAKES. ALSO, CRUISE CONTROL HAD NOT WORKED FOR NEARLY SIX MONTHS BEFORE FIRE.*AK