Ok Iain thank you for that. What saved my bacon was coming across the UHB with circuit diagram just as I was going to press as it were. Although I now have few other things to add in readiness for the next update!
A slight puzzle is this.
Mk 2 & earlier Gen Panels have a feed from the ignition to activate the field isolating relay, but it also carried the feed through to the generator connector, although the generator itself has no need for an ignition feed.
Mk 3 Panels no longer needed a field isolating relay, but none the less this ignition feed F PL2 to G SK1 still exists & has a bypass capacitor.
In the Rover harness panel to generator there is no feed G, but I notice it is depicted in the AEC harness. Quite why I don't know as there is nothing there that needs this feed.
Looking in an EMER I see a test bench described where a switch to the +ve rail can be operated simulating the ignition feed & it is marked "AXIAL STARTER"
So there is some vehicle that has a starter circuit permitted after activating a relay fed from the ignition feed that come out of G. It seems the only two other applications could be Stalwart or BV202. I have a Stalwart UHB but sadly there is no circuit diagram.
Perhaps a Stalwart owner can help out?