The instructions listed in the archives need to be corrected if you
intend to run your cabin light off the auxillary battery.  On my 90
Syncro Westy, the cabin lights are not connected to the two red wires in
the junction box behind the drivers seat. The two red wires only power
the fridge, water pump and water/battery sensors.  Here's how I did the
connection.
I installed a group 42 battery, which fit just perfect under the driver
seat.  I installed a plastic cap over the positive terminal to insure
the cover would not come in contact with it.  I used the VW stock
battery hold down device.  I followed the instructions in the archives
except for the camper lights.  My camper lights were connected to the
dome light above the drivers door.  After removing the camper shelf that
runs from behind the drivers seat to the rear of the camper, I cut and
capped the wires running from the drivers dome light.  While I had the
shelf out, I installed another interior camper light directly  above the
sink.  Rather than having to run two wires all the way to the junction
box, I ran the ground to the underside of the metal shelf.  I then
inserted the positive wire underneath the wallpaper and routed it down
to the junction box connecting it to the two red wires which are
connected to the auxillary battery.  My auxillary now powers my fridge(
when using 12V), sink water pump, sink sensor lights and the two camper
interior lights.  Seems to work great!  Roger Ehret, Gig Harbor, WA, 90
Syncro Westy.