That method is easy and cheap but does not supply the aux battery with
the full charging voltage seen by the main battery. The supply voltage
for the fridge relay comes from the dash fuse panel where it is reduced
by the length and size of the wire run as well as other loads that are
present on the source. It may still work ok, as long as your need for
the aux battery was so minimal as to make it more of a conversation
piece than a necessary upgrade.

If you wire one that way, turn on the headlights and run the fridge on
the 12 volt setting. Then measure the voltage on the main battery posts
and the aux battery posts. The much lower voltage on the aux battery is
why it will charge so poorly.

VW fitted some Vanagons with a factory aux battery. These used a large
wire directly from the main battery to the aux battery via a relay to
carrying the charging current. The shorter run of heavy wire charges the
aux battery faster and more fully.

The correct fridge relay contact to use if you do it that way is 30, not
87. VW reversed the usual high current leads for this application. They
used 87 as the always on contact instead of 30 so they could use the
other of the twin 87 leads to daisy chain the always on power to the
rest of the kitchen. (Bentley page 97.32b and 97.33b)

Mark

Roger Sisler wrote:

>I got the auxillary battery installed, ....In the end, if
>you have a westy , and want a auxillery battery, all you need is a battery
>(one without a vent), an 8 inch wire to go from the  existing relay to the
>positive battery post (contact 87 on the relay I think),2 hose clamps, and
>a  thin wire for the ground on the new battery.Just run 1 new wire on the
>87 contact to the battery, and from the positive post of the battery, run 2
>wires to the westy fuse box.That is  a total of 3 wires held onto the post
>with a hose clamp. That is it! Your done!
>
>
>