Try any green wire from the fuse box. Most if not all are fed by the ignition switch. I believe fuse 15 feeds the heater fan switch on such a green wire and may be convenient. What ever fused circuit you use, ensure the rating is upped to cover the extra load. I don't think the seat pads take much so an extra 5 amps on fuse rating should suffice.


Richard

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