What was found
PHX - AFTER TAKEOFF AND GEAR SELECTED UP, AT 4,000 FEET AND 230 KNOTS, CREW NOTICED THE RIGHT MAIN LANDING GEAR RED LIGHT WAS ILLUMINATED (GEAR HANDLE IN OFF POSITION). FLIGHT RETURNED TO FIELD AT PHX. WHEN GEAR WAS SELECTED DOWN, ALL THREE GREEN LIGHTS ILLUMINATED WITH NO RED LIGHTS. FLIGHT LANDED NORMALLY. CREW DID NOT DECLARE AN EMERGENCY. THE AIRCRAFT TAXIED OFF THE ACTIVE RUNWAY TO THE CARGO AREA AND THEN WAS TOWED TO THE GATE. MAINTENANCE REMOVED AND REPLACED THE RIGHT MAIN LANDING GEAR UP LOCK SENSOR S74 IN ASSOCIATION WITH MM 32-61-21. OPERATIONAL CHECK GOOD. SATISFACTORY GEAR SWING ACCOMPLISHED. ALL INDICATIONS NORMAL. SENSOR WAS FLUCTUATING 20 MHS WHEN IN THE NEAR POSITION USING LCR METER.