As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB, THE AFT CARGO DOOR WARNING LIGHT ILLUMINATED AND THEN WENT OUT. AIRCRAFT RETURNED TO IND AND LANDED WITHOUT INCIDENT. FOUND AFT CARGO DOOR NOT LOCKED CLOSED AND AFT CARGO DOOR WARNING INOPERATIVE. PROPERLY CLOSED DOOR AND MEL'D DOOR WARNING. AT DTW, ADJUSTED DOOR WARNING SWITCH STRIKER PLATE. OPERATIONAL CHECK OK.