What was found
AT FL380, MAIN CARGO DOOR LIGHT ILLUMINATED ACCOMPANIED BY "LATCH LOCK PIN NOT ENGAGED" ON DOOR CONTROL PANEL. A/C TURNED BACK AND DURING DESCENT LIGHTS REMAINED ILLUMINATED UNTIL CABIN PRESSURE WAS REDUCED TO MINIMUM AT WHICH POINT BOTH LIGHTS HAVE EXTINGUISHED. UPON ARRIVAL, MAINTENANCE FOUND THAT FORWARD LATCH PIN MICRO-SWITCH TRIGGER PLATE COTTER PIN WAS INFERRING WITH A RIVET TAIL ON THE DOOR SKIN DOUBLER. THIS WAS A POSSIBLE CAUSE FOR DOOR INDICATION. AFTER ACCESS TO THE AREA WAS PROVIDED BY REMOVING THE ACCESS PANEL, TRIGGER PLATE WAS FREED UP BY REPOSITIONING THE COTTER AND OPERATIONALLY CHECKED SERVICEABLE. SWITCH AND PLATE ASSY REPLACED AS A PRECAUTION.