What was found
AFTER GEAR SELECTION, AMBER "L DOOR" AND RED "LEFT" INDICATOR PER E/A CHECKLIST, LANDING GEAR ALTERNATE EXTENSION INDICATOR LIGHT IDICATED 3 GREEN, "GEAR SAFE FOR LANDING". REMOVED FROM SERVICE. CYCLED A/C POWER @ GATE. RED LIGT GEAR INDICATOR EXTINGUISHED AND LEFT GREEN INDICATOR ILLUMINATED. L DOOR AMBER LIGHT REMAINED ON. GEAR PINS INSTALLED.UPON A/C ARRIVAL @ GATE, L/H AFT GEAR DOORS WERE OPEN. REPLACED L/H MLG #1 DOWNLOCK SENSOR. NO FURTHER DEFECTS NOTED. RETURNED TO SERVICE.