As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF WITH LANDING GEAR SELECTED UP, LT MAIN RED (A) ANNUNCIATOR REMAINED ILLUMINATED WITH LOUD VIBRATION. SELECTED LANDING GEAR DOWN. AIR RETURN. LANDED WITHOUT INCIDENT. CLEANED A AND B SYSTEM PROXIMITY SWITCHES ON LT GEAR. TIGHTENED (A) SYSTEM PROXIMITY SWITCH CONNECTOR PLUG. LANDING GEAR EXTENSION AND RETRACTION OPERATIONAL CHECK NORMAL.