As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE TROUBLESHOOTING AN INTERMITTENT/UNCOMMANDED, ON OR OFF, OF THE AVIONICS MASTER RELAY - ELECTRICAL ARCING WAS HEARD. INVESTIGATION REVEALED ALTERNATOR OUTPUT 'A+' SHIELDED WIRE NR PA10A06 (BETWEEN FIRE WALL AND FORWARD END OF RF FILTER) HAD RUBBED THROUGH INSULATION OF WIRE NR PB11A06 (AT UNSHIELDED WIRE BETWEEN AMPMETER SHUNT AND HOT SIDE OF START RELAY). THIS SHORT CIRCUIT BYPASSES ALL CIRCUIT BREAKER PROTECTION.