The pilot reported that when he was inbound the passenger said that he could not hear him through the intercomm. Checks were made but the fault could not be rectified. The pilot said he then noticed considerable static on the radio and although communication with Mackay Tower was not good, he was able hear his landing clearance. There was no response from the flap indicator when flaps were selected, and no gear down indication after gear was selected down. He then activated the emergency gear extension valve, but still had no gear down indication. The pilot said he then assumed he had an electrical failure, and was not sure if the gear was extended or not. The aircraft was then climbed upwind on the runway heading to 1,000 ft. The passenger was aware that there was a problem with the aircraft and was becoming quite distraught and close to panic. The pilot attempted to contact the tower again on both radios without success, and squawked code 7600. After briefing the passenger comrehensively, and carrying out emergency procedures, the pilot landed the aircraft wheels-up on runway 14. The cause of the emergency gear extension failure could not be determined. When the aircraft was inspected by an engineer after the landing the emergency gear extension knob was in the up position. The engine was run on 6 July 1995 to determine the extent of the electrical problem, but no fault could be found.