What was found
MAIN CARGO DOOR ANNUNCIATOR ILLUMINATED AT 330. ENROUTE AT FL330, LEVEL FLIGHT, THE RED MAIN CARGO DOOR ANNUNCIATOR LIGHT ILLUMINATED. AN EMERGENCY WAS DECLARED TO ATC AND DESCENT/DIVERSION WAS INITIATED. EMERGENCY COM PROCEDURES WERE PERFORMED, ACFT GAVE NO OTHER INDICATIONS OF AN OPEN CARGO DOOR. APPROACH AND LANDING WERE CONDUCTED CONDITIONS WITHOUT FURTHER INCIDENT. MAINTENANCE COULD NOT VERIFY. R & R FWD LATCH LOCK PIN SWITCH IAW SUPPLEMENTAL CARGO DOOR MM 52-35-08. SYSTEM CHECKS GOOD IAW MM 52-35-08.