Let us know of your findings Ian. My money is on the switch itself. Inside I believe is an H shaped plate shifted up and down by switch action, joining contacts 7 and 8 in Off position and 1, 2, 3, 4 in On position.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone