It seems as though that 1960's Icon, the Dune Buggy is back. I'm thinking of the classic fiberglass body over VW chassis type item here, the traditional home-build project that was wildly popular at one time. If you're lucky enough to find one of these cultural relics to restore- congratulations !
We're not even going to discuss the myriad of sand rails, ATV's and modern imposters that are available new on the market today. Besides- those poseurs probably have all the wires that they need already.
There's plenty of resources online, and you may still find some stuff in the salvage yards. If most of the mechanical bits are there, and you've got a fuel supply and a battery, it should be easy to test fire the engine- just power up the coil and ground the engine block, look for the starter solenoid and give it a bump (electrical wise). If the wiring that's in place looks funky, begin by dis-connecting the harness that leads to the engine components before any experiments!
Watch out for 6 volt systems, they're still out there! It should run on 12 volts, but will probably fry the coil pretty quickly. It's OK to crank a 6 volt starter with 12 volts, so that can stay. Seriously though, it will be easier to make the change over to 12 volts as you begin a Dune Buggy project- Get friendly with a Starter/Alternator shop and and ask for a Generator (most old VDubs) that will fit your chosen or inherited engine. Our friends down at A and S Ignition will set the generator and regulator up on the bench and adjust everything for you, ready to bolt in- a very good investment if you want a reliable charging system. You could also convert to an alternator very easily and have a few less wire to deal with.
I'm guessing that most Buggies have home made wiring, a sort of hybrid of old VW harness and extra wires and bits that were added in as needed. If things look sketchy or just plain don't work, I'd say remove all the wiring and start from scratch- BUT- take a good look around and compare what you have to some basic VW wiring diagrams. There are a few variations, like which hi/lo beam switch do you have, which regulator, do you have a reverse switch, oil press switch etc. Be prepared to replace a few parts and all of the bulbs if it's a 6-12 volt conversion. For the time being, SAVE all of the VW connectors that go to the guages and such- you may have to re-use or replace some of these, and it may be hard to find exactly what you need. Unless you have plenty of wire on hand, you will need some sort of harness kit to start with. Chirco.com has an OK basic harness that gets most circuits covered for a fair price.
As you lay in the new wiring, remember that you really don't have a built in ground for most of the lamps and accessories- the body and dash is fiberglass. Start by getting the battery situated, and run a big ground strap to the engine/transaxle, and the positive to the starter. The main battery lead to the front lamps and dash and fuse box can come from the starter connection, make this wire a bit bigger than what was in there, maybe an 8 guage. This will flow plenty of current to keep the lamps bright, and allow for some add ons as you go. Meter from the battery ground to the front of the VW metal chassis, if this is a good ground, you can run all of the front accessory grounds back to the chassis. The basic harness really doesn't address the ground issue too well. Pick a good clean spot that you can bolt onto, and run the headlamp and signal gounds straight to it. Run another 8 guage up to the dash area, and create a stud of some sort that you can bolt all the rest of the front accessories to. One ground point will help to keep things neat, and be very handy when you need to add more circuits in the future.
Alltogether, this will be a pretty simple project, but take your time and allow for later additions. Be sure to place the fusebox in an easily accessible location ! Check out your online resources, and be sure to ask questions as needed. As always, test things out before you tidy up all the spaghetti and discover that you can't locate one particular wire !