What was found
AFTER TAKEOFF IN DEN, ON GEAR RETRACTION, LEFT MLG UNSAFE LIGHT REMAINED ON. GEAR HANDLE UP, GEAR DOOR LIGHT OUT. CYCLED GEAR AS PER POM, LEFT MAIN GEAR UNSAFE REMAINED ON. GEAR RETRACTION WAS EXTREMELY LOUD WITH A LOT OF VIBRATION. REPLACED LEFT MAIN GEAR UPLOCK PROXIMITY SWITCH. SWUNG GEAR SEVERAL TIMES, ALL INDICATIONS NORMAL.