<<Some vanagons did come equipped from the factory with a
 dual battery system. Some of these are also called campers
 in the Bentley, but appear to be weekenders. (no 3 way fridge)
 VW does list a relay called:
 Relay for 2 batteries.
 Part Nr. 411 915 511 B    Price a hefty 60.39
 ( maybe someone with a weekender camper with a factory
   dual batt. setup can verify this part number.)
 If the vanagon was factory equipped with a dual batt system, the
 second battery is shown in the Bentley diagram for that vehicle.
 The second battery is always conected via a
 6.0 mm2 cross section wire, to prevent overheating and insure
 efficient charging.
 Reference, Bentley 80-91 page 97.34a, 97.222, 97.225>>

This is accurate, part number and all, to what I have factory installed in
my van.