As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SEA - ON APPROACH LEFT MAIN GEAR DOWN INDICATOR DID NOT ILLUMINATE AND GEAR DOORS(L) +UNSAFE LIGHT REMAINED ON. ABORTED APPROACH. LANDING GEAR ALTERNATE EXTENSION GEAR DOWN INDICATORS SHOWED "THREE GREEN". FERRY TO PDX FOR REPAIRS. CHECKED PSEU FOR FAULTS AND FOUND LGDLK1. REPLACED LMLG NR 1 DOWNLOCK SENSOR AND HARNESS. CHECKS GOOD AIRCRAFT RETURNED TO SERVICE.