I spent yesterday poking about and generally trying to work out how it's
wired, and I found what I think is a relay linking the switched positives. I
guess this if were my VSR needs to go. I also intend to fit an AirX wind
generator to keep the batteries charged, so should I move this link to the
non switched side. Once again, thanks for your help.
I've updated the page http://www.jassira.com/battery_switches.htm with a few
more pictures.