A TBM800 pilot received three green and one red light indications after extending the landing gear. A safe landing ensued and Maintenance determined the red light was caused by a sticking gear unsafe switch on the left main gear.

Narrative

Upon extending the landing gear on final approach for landing I got a 3 green indication with a steady red light remaining on. I aborted the landing and as I flew by the Control Tower I asked them to visually check to see if the gear appeared to be down. The Tower confirmed that the gear appeared to be down. In this aircraft; a steady red light with 3 greens is not an unsafe gear indication. However; emergency checklist requires a manual gear extension.I then asked for vectors to a safe altitude and ran through the emergency checklist which included a manual gear extension. I powered to idle momentarily to see if a horn would go off that indicates that the gear is not down and locked and got no horn. I asked the Tower to have the fire trucks on standby for the uneventful landing.After landing I verbally gave the fire truck operator the info that he requested and contacted Maintenance Control to see if the plane could be flown safely back to our home base. In the meantime; our Manager of Flight Operations spoke with the TBM Service Center. Discussions centered on whether the gear was down and locked and in a safe condition. This was determined to be the case.The plane was flown gear down to our Maintenance base for troubleshooting. They put the aircraft on jacks and determined that it was a sticky switch on the left main gear that created the improper illumination of the steady red light.