AN SMA TWIN FLT INSTRUCTOR HAD AN ACFT EQUIP PROB GND WIRE TO THE R MAIN GEAR DOWN LOCK SWITCH PULLED OUT SHOWING THE R MAIN GEAR NOT TO BE DOWN. THE LNDG GEAR WAS LOCKED DOWN AND THE ACFT LANDED SAFELY.

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MY STUDENT AND I WERE PRACTICING LNDGS AT 4N1. WHEN I PUT THE GEAR DOWN ON DOWNWIND; WE DID NOT RECEIVE A R MAIN DOWN AND LOCKED LIGHT. THE GEAR WAS RECYCLED WITH NO CHANGE. WE THEN SWITCHED THE R MAIN LIGHT BULB WITH THE L. THE BULB WORKED IN THE L GEAR POS. WE THEN READ THROUGH THE CHKLIST FOR EMER GEAR EXTENSION. AFTER FOLLOWING THE PROCS; NO R MAIN GEAR LIGHT DOWN WAS RECEIVED. MY STUDENT AND I THEN BRIEFED EACH OTHER ON OUR INTENTION TO CONTACT CDW AND HAVE THE FIRE TRUCKS AWAITING OUR ARR. WE DISCUSSED LNDG ON THE L MAIN FIRST AND HOLDING THE R MAIN OFF AS LONG AS POSSIBLE. WE ALSO DISCUSSED JUST BEFORE TOUCHDOWN WE WOULD AJAR THE CABIN DOOR AND TURN OFF ALL ELECTRIC EQUIP. AFTER WE BOTH FELT COMFORTABLE WITH OUR PROCS; WE DID A LOW FLY-BY. THE TWR TOLD US IT APPEARED OUR R MAIN WAS DOWN AND LOCKED. WHEN TWR INFORMED US THAT THE TRUCKS WERE POSITIONED; WE MADE AN APCH. TWR AGAIN INFORMED US OUR GEAR APPEARED DOWN. WE LANDED WITHOUT INCIDENT. ALTHOUGH THIS SIT HAD HAPPENED 2 DAYS PRIOR; WE FELT WE HAD TO TREAT THE SIT AS THOUGH IT WAS THE FIRST TIME. THE GND WIRE TO THE DOWN LOCK SWITCH WAS DISCOVERED TO HAVE BEEN PULLED OUT. THE WIRE WAS REPLACED AND THE CORRECTION ENTERED IN THE LOGBOOK AND THE AIRPLANE FLOWN BACK TO HOME BASE. THE PROB FROM THE PREVIOUS INCIDENT WAS ANOTHER DOWN WIRE HAVING BEEN PULLED OUT WHICH WAS FIXED AND SIGNED OFF BEFORE THIS FLT.