What was found
(CAN) WHILE ENROUTE, THE MAIN CARGO DOOR WARNING LIGHTS ILLUMINATED IN FLIGHT DECK WITH AN ASSOCIATED AMBER, DOOR NOT CLOSED, LIGHT ILLUMINATED ON THE MCD CONTROL PANEL. CREW NOTED NO CHANGE IN PRESSURIZATION. ACFT DIVERTED. WHILE PASSING THROUGH FL260 THE LIGHTS EXTINGUISHED, AND THEN REILLUMINATED 5 MIN LATER. CREW DECLARED EMERGENCY AND CARRIED ON. MCD LIGHTS THEN EXTINGUISHED AGAIN WHILE FLYING THROUGH FL 140. MAINTENANCE ADJUSTED AFT DOOR CLOSED MICROSWITCH AND TESTED THE DOOR SERVICEABLE. ACFT DEPARTED.