Guitar Electronics for Musicians | Complete Guide to Guitar Design and Hardware with over 350 Photos, Drawing and Schematics | Essential Reference for Guitarists and Builders
From this book, you can learn more than you could ever have hoped to know about the design concepts and the practical details of the hardware used/made by guitar manufacturers all over the world.
A fantastic resource for any musician who wants to understand what's going on under the pickguard or behind the control plate of their guitar/bass without an electrical engineering degree.
Somewhere between being for an engineer and for the layman. It is short about 100 pages with schematics at the end. Definitely have a notepad and pen nearby. There is a lot of technical stuff and some math that might go over your head. While this could be a rough guide for electronics installations you might be better off learning through experience