Cars.
Billy, if you're familiar with automobiles, I'd suggest buying a shop manual for your car (or truck or whatever) and study the wiring diagrams it has. Start with some simple stuff (like anything electrical in a car is simple these days) like the trunk light or tail lights and work your way up to more complicated stuff. Actually, starting out with an older car made in the 1960's would be even better because the wiring was simpler and about the most complicated thing was a horn relay or starter relay/solenoid.
Dean