Information provided by the pilot indicated he had planned to land the aircraft in a paddock used by crop dusting aircraft. He contacted the owner of the paddock and determined that it met the requirements for his aircraft. The pilot was advised that a set of powerlines crossed the approach end of the paddock and he requested the owner to park his car underneath these powerlines to mark their location. When the pilot arrived over the strip a car was parked near the approach end where the pilot thought the powerlines were and he assumed the owner had acted on his request. After carrying out an Authorized Landing Area inspection during which he did not sight the powerlines the pilot made a normal approach. He kept well clear of the car but the aircraft collided with the powerlines on late final approach and touched down heavily. Information provided indicated that the owner of the paddock had parked his car more than 20 metres downwind of the powerlines for reasons which were not determined and this had given the pilot the wrong impression of their location. This accident was not the subject of an on scene investigation.