What was found
AFTER TAKE OFF, MX CARGO DOOR LIGHT ILLUMINATED.AIRCRAFT DECLARED AN EMERGENCY AND RETURNED TO ORIGIN. AIRCRAFT WAS GROUNDED BY MAINTENANCE. FOUND THE MCD DOOR DOOR NOT LATCHED LIGHT ON. OPERATED THE UNLOCK SWITCH UP, UNLOCKED DOOR AND POSITIONED THE CLOSED SWITCH DOWN. THE LIGHT EXTINGUISHED , OPERATED DOOR THRU ADDITIONAL CYCLES PER ABX MMS 52-32-00, NO FAULTS FOUND. PERFORMED OVERWEIGHT LANDING INSPECTION PER AMM 05-51-35 NO DAMAGE FOUND. AIRCRAFT RELEASED FOR FLIGHT.