What was found
LANDING GEAR DOOR OPEN LIGHT ILLUMINATED DURING DESCENT INTO DTW. COCKPIT OPERATING MANUAL PROCEDURES WERE ACCOMPLISHED WITH NO SUCCESS IN EXTINGUISHING LIGHT. CREW REQUESTED EMERGENCY EQUIPMENT ON STANDBY DURING LANDING AS A PRECAUTION. AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED BOTH MAIN GEAR DOOR SWITCHES. OPERATIONAL CHECK NORMAL. AIRCRAFT RETURNED TO SERVICE.