for those of you interested in running an auxillary battery setup here is a diagram of how to wire it in

http://www.melinga.org/dual_battery.jpg 

Its a good idea to put some sort of current limiting device on the feed to the second battery. If you drain your aux battery and then try and start most of the charge will be going to the aux battery not the starter motor. I have a auto reset cct breaker this way even if the aux is flat or faultly it will not suck the main dry of power

the switching relay only allows the charging relay to connect the batteries while the engine is running purely just for charging, the idea being I can completely drain my aux battery to run accessories for camping etc without interfering with my main battery , if the main battery does get low it cannot draw from the aux battery while cranking

Fair enough, must not have looked at the cct to close(late night)

heh, it happens all too often :beer

I have a 75 Kombi. Where di I find the charging relay and how do I run a positive to the engine compartment? What guage wire do I need. If you look from the back my main battery is on the right, do I put the second on the left ur both on the one side?

Ta Philip

you will need to buy both those relays ( $30.00 I think )
You can put your batteries anywhere, I have a T2.5 with the main battery under the drivers seat and I fitted my aux battery under the passenger seat. The cable I used was 6mm and all it does is run from the + terminal of your main batttery to the + of your aux battery
HTH's