As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INBOUND CREW REPORTED THAT THE EXTERNAL POWER LIGHT FLICKERED THROUGHOUT THE FLIGHT. WHEN ATTEMPTING TO HOOK UP EXTERNAL POWER SPARKS APPEARED AT THE PANEL. *S/D* EXTERNAL POWER CONTACTOR. REPLACED R56 EXTERNAL POWER CONTACTOR REF WDM 24-41-12, RAN ALL 3 ENGINES ON LINE CHECKS, NORMAL REF JRH. FOUND ONE CONTACT CLOSED ON OLD RELAY. NO HISTORY. ALSO REPLACED BUS PROTECTION PANEL, CHECKED GOOD.