What was found
(CAN) ON LANDING GEAR DOWN AND LOCKED, PILOT SELECTED FULL FLAPS AND THE RED LIGHT IN THE GEAR HANDLE CAME ON, WITH GEAR WARNING HORN ACTIVATED. AIRCRAFT LANDED OK AFTER TOWER CONFIRMATION OF GEAR DOWN. INVESTIGATION FOUND THE LEFT MAIN DOWN LOCK SWITCH ASSEMBLY HAD FAILED. SWITCH REPLACED, BUT THEN FAILED AGAIN A COUPLE OF DAYS LATER. REPLACED AGAIN AND OK THIS TIME.