I'm not a landy owner, but I have a classic dub and do all my own electrical work. Do you want it specifically stock wiring (Is there such a thing?) or are you just after a general way to run a 12v slpit charge? If so, you just need an automotive relay, a wire from your alternator (So it only charges when you're running), and a wire from your drive battery. Here's a nice page for that sort of stuff:
Alternatively, if you just want twin batteries to double capacity for restarts etc then you just need to bang them in parralel. I.e. - run a pos lead from your original to the new battery pos and ground them both. Not sure if there's many benefits to that, but I don't do Landys so forgive me if I'm missing something.
