> I've posted my findings and sketched up my =
> aux. battery wiring in this post on my blog

Alistair:
Maybe you are not old enough to know about KISS....  ;-)

Normally, here, I'd explain how I DO IT.  Of course, you already
have how YOU DO IT, which you have fixed, so I'll omit mine.
Even so, we love your shufti posts!

Richard