What was found
ON LANDING, WHEN GEAR SELECTED DOWN, 3 GREEN DOWN AND LOCKED LIGHTS ILLUMINATED. SHORTLY AFTER, LT DOWN AND LOCKED LIGHT EXTINGUISHED. PILOT WENT AROUND AND EMERGENCY EQUIPMENT DISPATCHED TO THE RUNWAY. ACFT LANDED WITHOUT INCIDENT. UPON INSP, LT GEAR DOWNLOCK SWITCH FOUND TO HAVE NOT BEEN SAFTIED. JAM NUT CAME LOOSE AND DOWNLOCK SWITCH BACKED OUT IN ITS HOUSING.