As a complete electrics numpty I've been looking for a dummies guide that would spell out the basics for me and I think I've found it in the Beginners Guide to Motorcycle Wiring by John Partridge.

The document is downloadable/printable from that URL but it's also worth checking out JP's website. He looks to be a very interesting guy (read that as probably eccentric in the true British tradition) who's written on subjects as diverse motorcycle wiring, teeth care and building your own steam engine!

Not as comprehensive as JP's guide, Basic Motorcycle Wiring by 750ACE, presumably from a KTM forum, also looks like a good starting point.

Tim