What was found
MIA - FLT 63 - AFTER TAKEOFF MIA WHEN LANDING GEAR RETRACTED, LEFT MAIN LANDING GEAR RED AND GREEN LIGHTS REMAINED ILLUMINATED. AIRCRAFT RETURNED TO MIA AND LANDED WITHOUT FURTHER INCIDENT. CHECKED WIRING FOR LANDING GEAR DOWNLOCK SWITCH AND CHECKED LANDING GEAR INDICATION SYSTEM. COULD NOT DUPLICATE ON GROUND. PRECAUTIONARY REPLACED LANDING GEAR ACCESSORY BOX AND CHECKED ALL ASSOCIATED SWITCHES. ACCOMP LANDING GAR RETRACTION CHECK. SYSTEM GROUND CHECKED NORMAL OPS. (M)