Greetings,
With regard to relays in "campers":
"3-way refrigerator relay":
The 2 vanagon full westfalia campers ('81 and '90)
that I have owned only had the little "refrigerator relay",
as shown on page 97.33b in Bentley.
That relay (called 12 volt refrig./heater relay) is mounted
under the driver's seat.
In my opinion, that relay is not intended by VW to
also run an aux. battery in addition to the refrig.heating element
(which actually can draw quite a bit), even though
it is mounted in that empty battery box.

"Auxillary battery relay'':
The "auxillary battery relays" mentioned in the Bentley:
(In my Bentley, they are on pg.97.34a, pg.97.222, and pg. 97.225.)
These relays are intended for a second battery, and are
designed adequately by the german engineers for that purpose.
The point is that those relays are different from what we have in the
full westfalia camper with the 3-way refrigerator.

The 2-battery setup with that stronger relay is what VW
used on the "weekender camper", that has only an
electrically powered refrigerator.
Those vanagons probably were delivered with 2 batteries in place.

If someone wants to convert their westfalia full camper to
a dual battery setup with a relay, they could go to the dealer
and purchase that stronger relay that is shown with the dual battery setup.
And then install the bigger size wire, and perhaps install
an additional 30 or 40 amp fuse, and that setup should be ok.

In summary, all that I am saying is that the "refrigerator 12 volt
heater relay" for the 3 way frig. is not the same part (and not as strong)
as the dual battery relay used for the weekender package electric only
refrigerator.

Harald
'90 full camper westy