Ok, here is the info you seek. (including the year of vehicle in
question may help in getting answers sooner)

You don't need to remove the fuse box, just the cover so you can get to
fuse #3.

Fuse #3 always has 12 volts at the top leg and then the fuse connects it
to the bottom leg.

1. REMOVE fuse #3.
2. Put a male .250 spade connector on the end of the wire coming from
your aux batt. (use ~12 gauge wire and an inline fuse in that wire near
the aux batt)
3. Plug that male spade into the lower leg hole of fuse position #3.
(fuse #3 was removed, see 1. above)
4. You are DONE!

I am assuming that this is a 86 or newer Vanagon. Earlier years need
different though quite similar instructions. This will put all interior
lights, radio, and cig socket on the aux battery, protected by the new
inline fuse you placed in the wire. Fuse #3 is gone, never to return.

Mark

Malcolm Stebbins wrote:
>
> I hope you get an answer to this, as I want to do the same thing.
> Malcolm
>
> > Right off, however, I can not see where to connect the new wire to the
> > #3 circuit at the fuse box.   Do I have to remove all of the relays and
> > fuses and open the fuse box further to continue? If so, do those of you
> > who are fuse box savvy have any cautions, insights, or tips besides
> > ground strap disconnections in advance of the work? Thanks in advance.
> > Al