What was found
DURING GEAR EXTENSION RECEIVED THREE GREEN MAIN LIGHTS & ONE LT RED LIGHT. AFTER MISSED APPROACH IT BEGAN TO FLICKER, IT FLICKERED FOR THE WHOLE NEXT APPROACH WHICH LED TO AN ATC ISSUED GO AROUND & STOPPED FLICKERING SHORTLY AFTER. CHECKLIST WAS EXECUTED & GEAR CONFIRMED SAFE, STANDBY GEAR INDICATORS SHOWING TWO GREEN. JACKED ACFT & PERFORMED GEAR RETRACTION. DUPLICATED DISCREPANCY ON FIRST TWO CYCLES. FOUND LT GEAR UNSAFE SWITCH WITH DIRT & SLUDGE BUILD UP. MANUALLY MOVED SWITCH & FLASHING UNSAFE LIGHT WENT OUT. CLEANED SWITCH & PERFORMED ADDITIONAL 10 CYCLES & OPS CHECKED GOOD. PERFORMED IAW MM 32-30-11.