As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RDD FLIGHT: AFTER SELECTING GEAR UP AFTER TAKEOFF, ALL GEAR LIGHTS EXTINGUISHED EXCEPT FOR THE 'R-DOOR' AMBER LIGHT. FOLLOWED EMERGENCY CHECK LIST STAYING UNDER 185 KTIAS. PERFORMED ALTERNATE GEAR EXTENSION FOR EMERGENCY CHECK LIST FOR SUBSEQUENT LANDING. MAINTENANCE, AFTER TROUBLESHOOTING, REMOVED AND REPLACED RGUPLK, RGDLK, AND RGDLK2 PROXIMITY SENSORS PER Q400 AMM TASKS 32-61-06-000-802 AND 32-61-06-400-802. FUNCTIONAL TEST WAS GOOD. NO PARTS REPLACED. AIRCRAFT RETURNED TO SERVICE.