, a Piper Cheyenne, was on final at Thompson (YTH) when the crew initiated a go-around. When queried, the pilot indicated they needed to re-cycle the gear and no asistance was required. During a circuit, the crew attempted to re-cycle the gear, and after 2 attempts they advised they were still getting an unsafe left main gear indication. Emergency standby was initiated and the crew advised they would do a fly-by of the FSS cab. The gear appeared to be down during the fly-by. The city fire department and the airport duty person had been called out and were enroute. The crew elected to land and did so safely at 2140Z. Response personnel arrived shortly thereafter while the pilot disembarked on the runway to confirm that the gear was safe for taxiing. The pilot re-boarded the a/c and taxied off the runway without incident at 2144Z. TSB later reported that maintenance discovered a broken wire in a landing gear microswitch.