The flight was scheduled as a dual instrument training flight. As the student brought the aircraft to a stop prior to the engine run-up the gear-up warning horn momentarily sounded and the gear-up warning light flashed once or twice. The instructor took control and checked the landing gear warning systems. As he could find nothing wrong and he could not reproduce the momentary warning signals he deduced that it was safe to proceed with the flight. He did decide to test the integrity of the gear warning system before returning to the Jandakot circuit area. The flight proceeded normally with all landing gear indications and warnings operating correctly during the departure, an instrument approach and overshoot and a practice engine failure. During a second approach the landing gear did not extend when selected down. Following a period of trouble shooting the landing gear was extended using the manual extension system. Three green lights were obtained and the aircraft was landed at Jandakot. As the aircraft cleared the runway, the gear unsafe horn started to sound and the gear-up light started to flash. The pilot stopped the aircraft, confirmed that the three green position lights were indicating down and locked, the landing gear lever was in the down position, the gear motor circuit breaker was out and that the gear relay circuit breaker was in. Whilst he was visually checking the circuit breakers, the gear motor momentarily made a sound. The pilot considered shutting down the aircraft but before he could take any action the aircraft gently rocked and the right main landing gear collapsed. The three green gear down and locked lights were still illuminated. Subsequent investigation disclosed that the landing gear motor relay contacts were fused together creating a permanent landing gear up circuit.