As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN LANDING GEAR WAS EXTENDED THE LEFT MAIN GEAR GREEN LIGHT FAILED TO COME ON. NO RED LIGHT. ALL LIGHTS TESTED NORMAL. CREW ACCOMPLISHED VISUAL CHECK OF GEAR EXTENSION. LANDED NORMALLY. FOUND A BAD CARD IN THE PROXIMITY SWITCH CONTROL BOX. REPLACED THE BOX. CHECK-C 10-14-99 MCI.