Edward, DON'T do it that way. The stock aux bat wiring is not large
enough to safely allow the aux battery to be connected during starting.
The starter motor can draw way too many amps for that small wire. That
is why VW connected the relay in such a way that it is not connected
unless the alternator is charging. They even hooked the controls for the
relay to the starter circuit such that it disables the relay when you
are trying to start. They did this as a double safety precaution.

In other words VW designed the stock aux bat system to prevent exactly
what you wish to do. Don't simply bypass their protection measures.

You need to upgrade the relay and the wires that connect to it from each
battery. To do less is very risky. You may get away with it for a time
but it disaster may ensue.

Mark

Edward Maglott wrote:
>
> I was looking at a way to hook the aux and vehicle batteries of the Westy
> together.  I have a charger set up on the aux batt, so that it gets charged
> whenever the vehicle is plugged in.  I would like to connect the two so
> that the vehicle batt can share in that charging when needed.  Or let the
> aux batt boost the vehicle batt when needed.  So I thought, there's already
> a relay in place to do this.  How about a little switch to energize the
> coil on that relay?  I tried applying 12V to the blue wire and that did the
> trick.  So then I started to find a switch to install for the purpose.  Now
> I am thinking about where that 12V is going to go when it also travels back
> down the blue wire to the alternator.  Is this a bad idea?  Thanks for any
> input.
>
> Edward