Went to take the Mini to the dentists, unlock the car, get in, go to start it, and all electrics in the car die. Nothing works. Looks like I know what I am doing when I get home.
Update: the negative terminal had slipped enough so that it was right in the edge of continuity and arcd, blowing the fuse. Replace fuse, discover it’s still not working, and adjust the terminal and the Mini is back up and running. Mayby this will fix the intermitant dash resets I was getting.