Thanks for update Laurens. Fuse 9 feeds to stalk switch (mode select) on G41 and instruments G42, both solid green cables.
Very slowly building up a picture of how everything works and then in a better position to understand what is wrong with yours.
Still an inspired guess but wonder if the immobiliser could be at the route of the problem. Thoughts based on the fact it handles keep alive circuits as well as those operated by ignition key. There is a shorting plug available that replaces the immobiliser for customers that didn't order that option (although many did). It provides four loops on eight pins and would be easy to make, but you would need a blank plug. Alternate may be to try immobiliser from your other car if feasible.
Richard
2018 Roadster 3.7 1966 Land Rover S2a 88 2024 Royal Enfield Guerrilla 450 1945 Guzzi Airone