As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SECOND INCIDENT, WARNING LIGHT FOR LOWER AFT CARGO DOOR ILLUMINATED AFTER TAKEOFF DURING FLAP RETRACTION. DUMPED FUEL AND RETURNED TO DEPARTURE STATION. WHEN FLAPS EXTENDED TO 20 UNITS LIGHT WENT OUT THEN BACK ON. LIGHT EXTINGUISHED DURING LANDING GEAR EXTENTION. INSPECTED DOOR WIRING FOR SWITCH, DOOR RIG.