Sorry but I missed the beginning of this thread.  I read Tom's reply about a
switch available at a marine/boating supply house.  This sounds pretty useful to
me. 

My '90 Westy has a dual battery setup with some things that don't seem to make
sense.  I think the PO made some mods and didn't bother to document them in any
way.  The dealer and Bently both say there is supposed to be a bypass relay
installed.  Does anyone know where this relay used to live?  What it bypassed?
How was electrical distribution between the batteries originally configured?

I think (couldn't be sure) that the second battery currently runs the
refrigerator even with the ignition off if you want it to all the time (if
battery is selected)  and the main battery does everything else.  It would be
much more useful to have the main battery reserved for engine only and to have
all the lights, the furnace (I just installed it) and the water pump coming off
the auxillary battery without risk of not being able to start in winter.  As the
idea is to use the camper for some fairly serious back county cross-country
skiing it would be really scary to get stuck.

Clark
'90 Westy in search of blue skies