What was found
HELICOPTER HAS BATTERY BOX BOLTED TO COMPOSITE FIREWALL. BATTERY BOX IS NOT GROUNDED TO BATTERY. A REGULATOR RECTIFIER AND STARTER RELAY ARE GROUNDED TO BATTERY BOX. A SCREWDRIVER WAS ACCIDENTLY DROPPED INSIDE OF BATTERY BOX TOUCHING POSITIVE TERMINAL. SCREWDRIVER THEN GAVE BOX A POSITIVE CHARGE COMPLETING CIRCUIT THROUGH THE NEGATIVE WIRE OF THE REGULATOR RECTIFIER AND THIS CAUSED A DEAD SHORT AND WIRES TO CATCH FIRE.