Isolating key switch

[halloween]

On my old FPM the wiring is a bit of a birds nest. I want to reinstate the isolating keyswitch and red (Presumably charging) lamp that are fitted but redundant. Which wire do I need to put the switch and lamp in in order to make the switch and lamp work again? Please tell me in terms of "the wire that goes from A to B" rather than "the blue one" because all my wires seems to be orange!

Thanks