Hi volks,
Since I've had numerous requests for the battery cut-out
relay installation instructions, I thought to repost the
instructions that I previously posted in early 1999.
In light of the recent discussions, the wire sizes have
been reduced slightly. Basically #8 awg wire has been
reduced to #10 or #12 awg wire. Everything else is
basically the same. If you already received this from me
directly, just delete.
Harald
'90 westy

About dual battery systems:
Different options:
1) A manual batt. switch can give you more flexibility.
You can switch between different batteries.
Drawback, one always has to switch back and
forth, to use the aux. batt., or to charge the aux batt.
The vanagon "Adventurewagen" has such a system.
It can be more expensive and time consuming to install.

(or)
2) A battery cut-out relay is very simple and relatively
inexpensive to install.
It would be helpful to take a look at a Bentley diagram
of a weekender vanagon with a dual batt. setup,
Some weekenders were factory-equipped with a dual
battery system.
The GL full camper vanagons did not come with such a
system installed. In the diagram you can see the aux. batt.
and the main batt. It actually is a very simple diagram.

(or)
3) It's also possible to use a battery isolator, but the
only I know that's proven to work with the vanagon
is made by Sure Power Industries, and it's model 1202R.

Things you might need for a battery cut-out relay installation
in a vanagon gl westy camper:
1)  A section of # 12 or 10 gauge, long enough
     to go from one battery to the other.
     VW uses a 6.0mm that is close to  # 10 gauge wire
     in some of the weekenders.
     You also need a short section of  # 18 gauge wire.
2)  one 12 volt heavy duty 30  relay.
3)  one 12 volt 20 to 30 amp fuse or
      optional 12 volt 20 to 30  amp circuit breaker
      or a 20 to 30 amp auto reset breaker.
4)   at least 4 ring terminals, for the #12 or #10 wire, to connect
      the wire to the relay and the fuse or breaker.
5)   one batt. ground strap. For the aux. batt.
6)   one batt.-terminal-connector to use with the # 12 or #10 wire,
      for securing it to the + terminal on the aux. batt.
     You also need a connector to fasten the other end of the wire
      to the + terminal on the main batt.
7)   Two quick splice connectors for small #18 ga. wire,
      and two female connectors for # 18 ga wire. The female
      connectors have to fit the small terminals on the new
      "Battery-cut-out relay".
      (you need this to connect the new battery-cutout-relay
       to terminals 85 and 86 on the existing refrigerator-12 volt-
       heater-relay)  under the driver seat. ( GL camper)
      If you look carefully, you will see tiny numbers stamped
      next to the contacts on the frig. relay.
      See diagram for camper with 3 way frig in Bentley.
      These wires are used to trigger the new relay, that is, to
      make the battery cutout relay go on and off.
8)  some plastic ties, and electrician's tape and
     a few sheet-metals screws.
     The sheet-metal screws are for fastening the new relay in place.
9)  a couple of rubber grommets, for routing the 12 to 10 awg wire
     through sheet metal.
     My guess, total cost of all this maybe $25 to $50.
 Optional:
     A section of flexible conduit to protect the wire when routing under
     the vanagon. I usually use a piece of clear vinyl hose, to protect the
     wire from chaffing, where it contacts the body. If the hose is
     watertight, make sure it will not collect water.
     Buy some electrical putty (home dep.) to seal holes you might have
     to drill or to route the wire.
     I wonder what I forgot. Oh... the aux. battery.
     To put all this stuff together is another post.
------------------------------------------------------------------------
How to install the battery cut out relay. Second part.

To be on the safe side, you can purchase a relay for 2 batteries
from the VW dealer. It would be the most proven to use with the
trigger wire. VW uses such a relay in some vanagon weekender
models in the U.S.  It costs $62.
But there are other sources for similar relays.
A good reference and diagram is in 1991 Bentley on page 97.34 a.
There you can see both batteries drawn in the diagram and
the battery cut-out relay.
In this application VW used a 6 mm2 wire from the main to the
aux. battery. For a safe installation, one should not use a wire
much larger than the 6 mm2 wire VW used.
This battery relay was not factory installed in the westy camper
with the 3 way refrigerator.

This is how I would install the aux. batt. charging circuit, if I
would use a relay.
Of course, there are alternative options.
Note:
Do not use a relay that would overload the two trigger wires.
The relay should be just the right size for the application.
Not too small and not too big. It should be able to handle
30  amps continuously, and not overheat.

This is  how the new battery-cut-out-relay
should work.
1)   Engine running: Both batteries are connected. Aux. batt.
                              and main batt. are charging.
2)   Engine turned off: The aux. batt. is disconnected from the
                                  main battery.
3)   Ignition turned on:  The two batteries are still disconnected.
4)   Starting the engine:  The two batteries are disconnected.

Nr. 4 is important, since the system discussed is only designed
to charge the aux. battery, and not for starting the motor.
VW installed a relay trigger circuit in the camper.
(Trigger circuit means, it switches relays on and off).
One can use this circuit for the new batt.-cut-out-relay.
This will ensure, the batteries are not connected, while
the engine is started.
It is located at terminals 85 and 86 on the existing refrigerator
relay, under the front seat in the westy camper.
The existing refrigerator-12-volt-heater-relay stays as is.
We only tap into the two small wires, (terminals 85 and 86)
to also control the new batt.-cut-out-relay.
To alter the fridge relay could drain the battery very fast,
if the engine is not running.
Summary:
You have to route a new #12 to 10  wire from the + on the
main battery to a breaker, then to a batt.-cut-out-relay, and
then to the + terminal on the auxiliary battery.
The new  batt.-cut-out-relay   is triggered by the two
small wires, on terminals 85 and 86 on the factory installed
refrigerator cut out relay.
The installation:
1) Take out the front seats, and gain access to the front batt.
    boxes. One on each side. Test fit the aux. batt. in its box.
   If you use a Optima, the terminals should be to the back.
   You should have enough space on the right side of the
   aux. batt., to install the new cut-out-relay, and the breaker
   or fuse.
   Also mark where to fasten the batt. ground strap to the
   frame, and mark a place, to drill a hole for the #12 to 10 wire.
   Note the fuel lines, AC hoses etc under the batt. boxes.
   Take your time.

2) Take aux batt. out and drill the hole for the #12 to 10 wire.
    Remember to use a grommet where it passes through the sheet
    metal.  Mount the cut-out-relay and the fuse on the right
   side in the aux. batt. box.
   I suggest you install a piece of sheet plastic between the
   new relay/breaker, and the battery box, so the wires later
   don't rub against the metal.
   Use the sheet metal screws for fastening.
   Install  the ground strap to the frame in the batt. box.

 3)Cut two pieces of  # 18 ga wire, and crimp one
   female connector to each and connect them to the trigger
   circuit on the  batt.-cut-out-relay.
   Note:  The new relay should have 4 terminals. The smaller 2
   terminals should be for the trigger.
   (one of them might be marked as ground, do NOT ground)
   Find the 2 small wires that go to terminals 85 and 86 on the
   refrigerator-cut-out-relay. Look in the Bentley for  the colors
   of these wires. In the 90 westy they are 1) blue 2) red/black
   Use two quick-splice-connectors to connect
   them to the trigger terminals on the new cut-out relay.

4)Use the ring terminals to connect the #12 to 10 wire.
   As the wire enters the aux. batt. box, first connect it to one terminal
   on the 30 amp breaker. Cut a short section, to connect the
   other terminal on the breaker to one of the big terminals on
   the new batt.-cut-out-relay.
   Now connect a long enough section of #12 to 10 to the remaining
   big terminal on the batt.-cut-out-relay. This end goes to the
   + terminal on the aux. battery. But for now, wrap the end
   in some plastic, so it does not make ground contact.
   Make sure the connections on the new relay and breaker
   don't make any ground contact, and are safe.
   Use tape, shrink tubing etc. to protect them.
   Route the #12 to 10 wire under the car to the main battery box.
   Use cable ties to secure it, and make sure there are no
   sharp objects near the wire. Preferably use a conduit,
   to give it some added protection. Give the wire lots of
   slack.

5) Find or make a opening in the main batt. box, to
   enter the other end of the # 12 to 10 wire. Again use a grommet.
   As an option, you can install a second 30 amp breaker
   or fuse with the # 12 to 10 wire next to the main battery.
   To reinstall the main battery:
   Important. Make sure the loose end in the aux. batt. box
   does not make ground contact. (wrap with insulating
   tape, or a plastic bag).
   Now reinstall the main battery, and connect the new #12 to 10
   wire  to the + terminal on the main batt. Leave the ground off, till
   you are finished on the other side.

6)Install the auxiliary battery.
   Unwrap the #12 to 10 wire, the one that comes from the
   cut-out-relay, and connect it to the + terminal on the
   aux. battery.
   Now connect the ground strap to the - (minus) terminal
   on the auxiliary battery.
   Go to the other side of the car, and connect the ground on
   the main battery.

   To test the operation of the relay:
   Disconnect the new #12 to 10 wire at the main battery + terminal.
   With the engine off, there should be no current and no ground.
   Reconnect the #12 to 10 wire.
   On the aux. battery:
   With the engine running, the voltage should be higher.
   (battery is charging)
   Engine off, voltage drops.

Note:
Keep in mind that for standard wire sizing, as the number
becomes smaller, the wire becomes bigger.
Example, 10 awg is bigger than 12 awg.

The auxiliary battery compartment in the westfalia camper
is not vented. It is possible to add two vents. Otherwise
one should use a sealed battery to prevent the build up of
fumes. A deep cycle battery will last longer
and give better service.
Now you are ready to connect the appliances to the aux. battery.
But that's another story.

      Note: Disclaimer: You should double-check everything
      with a professional auto electrician. I might have made a mistake.
      In my own westy, I installed a battery isolator, so I have no
      long-term experience with the relay setup.
      But the relay installation is fairly simple and straightforward,
      and VW installed such a system in some vanagon weekenders.

Good luck.
Harald
90 westy