What was found
DURING APPROACH INTO DTW, LANDING GEAR DOOR OPEN LIGHT REMAINED ON AFTER GEAR EXTENSION. CREW EXECUTED GO-AROUND PROCEDURES AND RECYCLED GEAR. NORMAL INDICATIONS WERE ACHIEVED. AIRCRAFT LANDED WITHOUT INCIDENT ON SECOND ATTEMPT. DISCREPANCY COULD NOT BE DUPLICATED BY MAINTENANCE ON GROUND. REPLACED LEFT AND RIGHT MAIN GEAR DOOR SWITCHES AS A PRECAUTION. OPERATIONAL CHECK NORMAL. AIRCRAFT RETURNED TO SERVICE.