What was found
MAIN POWER WIRING HARNESS PASSED THROUGH 2 INCH DIAMETER HOLE IN HORIZONTAL ALUMINUM INSTRUMENT PANEL SUPPORT STRUCTURE. THIS HOLE IS LOCATED BEHIND FIREWALL APROXIMATELY 10 INCHES AND APPROXIMATELY 1 INCH FROM PILOT'S SIDE OF FUSELAGE WALL. THIS HOLE WAS NOT INSULATED WITH RUBBER OR NYLON GROMMET MATERIAL AND WIRE HARNESS HAD RUBBED THROUGH THE INSTALLATION AT APPROXIMATELY 10 WIRES AGAINST SHARP METAL EDGES OF THE HOLE.