What was found
DURING FLIGHT, THE CREW REPORTED THAT THE MAIN CABIN DOOR ANNUNCIATOR ILLUMINATED. DIVERTED FOR FURTHER INVESTIGATION AND REPAIR. LANDING WAS UNEVENTFUL. TROUBLESHOT TO DETERMINE THE CAUSE. THE AIRCRAFT WAS GROUNDED. DISCOVERED THAT A BELLCRANK IN THE MAIN CABIN DOOR ASSOCIATED WITH A DOOR UNLOCK SWITCH WAS FOUND CRACKED. THE PRESSURIZATION OF THE AIRCRAFT CAUSED THE BELLCRANK TO FLEX AND AFFECTED THE CORRECT OPERATION OF THE DOOR UNLOCK SWITCH AND GIVING A FALSE UNLOCK INDICATION. A NEW BELLCRANK WAS INSTALLED AND RIGGED. OPS CHECKED SATISFACTORY. THE AIRCRAFT WAS RETURNED TO SERVICE.