VH-WIL was operating in the circuit area at Port Lincoln for the purpose of testing the installation of a Mogas conversion. The LAME who had carried out the work was the pilot-in-command. He was accompanied by the owner who was seated at the right hand control position. After entering downwind for a touch-and-go landing on runway 23, the pilot, while testing the new fuel pump switch, inadvertently selected the master switch off. When the master switch was reselected, the VHF radio, which had been set to the MTAF frequency, defaulted to 121.5 Mhz. The pilot then selected an incorrect frequency. At the same time, VH-LNB taxied and lined up on runway 19 for departure to Adelaide after making all the necessary radio calls. VH-WIL made an approach and landed just past the threshold of RWY 23. As the pilot applied power again for take-off, the passenger sighted VH-LNB rolling on RWY 19. The pilot of VH-WIL aborted his take-off well short of the intersection of the two runways, selected the correct frequency and called VH-LNB.
