Jack,
A bug diagram will only go so far...and may be slightly confusing. There are lots of postings at the Samba as previously indicated. I've used 8 circuit systems which are available on EBAY with good success. 12 circuit models are also available. They don't have everything, but they are an affordable starting point.
Remember, everything on the Buggy needs to be grounded. On a standard VW the grounds are picked up by the metal bodies on lots of circuits.
Here is my 8 circuit on my old Manx. It was fully functionable (horn, wipers, lights,etc) and had 2 circuits left over.
happy to answer any questions you have.