OK; got the trim off, pulled back the carpet and found ...
... a metal plate covering a plastic box. Got the metal plate out but couldn't unclip the door as it's extermely awkward to see and get to behind the other plastic box there.
I'm too tall [6ft plus] and too old [60 plus] to stay bent there long enough to persist without hurting my back, so someone else will have to get the door open for me.
Interestingly, I assumed the other connector in the picture was the alternator output but the fuse is only 60A. Discovered later that it's the radiator fan.
So does anywhere know where the alternator output connects so as to send its output down to the battery?
Julian