The diagrams are available on the pelican main page.
I have spent hundreds of hours reworking the electrical system in my 911E and would offer the following advice:
1. The diagram is your friend. Everything can be traced out if you have patience, at first it looks like a bunch of spaghetti but after working with it for a while you realize the engineers at Porsche did a pretty good job of designing it.
2. Always, always use the same color wire to replace burnt or missing factory stuff. I actually went to the trouble to get original german wire, red with a black stripe, from the folks at
www.ynzyesterdaysparts.com. If you are contemplating a total restoration, they actually make complete wiring harnesses, concours quality, as original. I've even seen them complimented by Kevin at Gunnar Racing. Ditto the brass "faston" connectors and rubber insulation, these are just like the factory did, not some cheapie aluminum terminals with a plastic crimp.
3. The wiring harness can be cleaned off with lacquer thinner, often wires get painted over.
Not having a '68 handy anymore I can't give you specific advice. I have some pictures of a 67 s from a concours at home, I'll check them to see if they illustrate anything.
Good luck!