I devised these sections up really weird. A whole post devoted to pickups? Well, at least you know pickups really well now. That means I can get started on electronics.
With your standard Fender Telecaster, you'll have a volume knob, a tone knob, and a 3 way selector switch. I believe Strats have two tone knobs, one for the neck and middle pickup and one for the bridge (which is just stupid, but someone thought that was a good idea.)
Ok, first off, let's take a look underneath the pickguard and control plate. (Again, I am modeling after the Telecaster, but principals are still the same.) Here you'll see all the things that will make you want to be extremely careful.
Some knobs are screwed on by a little screw in the side. You can see one in the picture. These don't pop off. You get a tiny flat head and loosen the screw and it comes off very easily.
Moving on! What makes the volume knob volume? A potentiometer is a variable resistor, which means you can control how much signal it is stopping. If the volume knob is turned all the way up the signal flows freely and as loud as possible. When the volume is turned off, the potentiometer is sending all of that signal to ground (anything metal, as long as it is connected somehow to the other grounding points) so that no signal is coming through. The way the signal increases or decreases depends on the type of potentiometer you get. (I recommend 250K-500K Ohm Audio Taper pots.)
Tone! What is actually happening when you turn the tone knob? Well, it's actually very similar to a volume knob, except one thing. Instead of sending signal to ground when the tone knob is turned all the way down, a capacitor is connected to ground so that all of the signal is filtered through it before it's sent to ground. This will filter out the high frequencies, which some people like. The amount of high frequencies you cancel out depends on the capacitor. (I recommend a 47uF capacitor. Not too much, not to little.) When the tone knob is turned all the way up, no signal is being filtered, so you hear the untampered signal coming straight from whichever pickup is selected.
Wiring 2 pickups to a 3 way selector is easy. The way telecasters are wired have the neck on position 1, neck and bridge on position 2, and just bridge on position 3. Strats are basically the same, but with 3 pickups and a 5 way selector switch. Neck on 1, neck and middle on 2, middle on 3, middle and bridge on 4, bridge on 5. The way you wire this is simple. First take your selector switch and place a wire connecting the two top left and two bottom right tabs on the selector switch. This wire will go to the volume potentiometer. After that, the neck pickup positive wire (colored) goes to the top right tab, and the bridge pickup positive wire goes to the bottom left tab. (This way when you select position 2, the wire going to the volume pot will be connected to both the neck and the bridge. Then wire all of the ground (black) wires to ground. (Usually on the top of a potentiometer.)
Much easier in a picture.
Everything you connect to "ground" has to be connected together. So wire the tops of each potentiometer to each other. Wire the capacitor for the tone knob to the top of the tone potentiometer. Wire the ground prong from the volume knob to the top of the volume potentiometer. Wire the ground wires from the pickups to the top of the potentiometers. Wire the shield from the input jack to the top of a potentiometer, and wire the top of the potentiometer through a hole in the guitar to be squished underneath the bridge plate. This connects the ground to the bridge, the strings, the tuning pegs, and all things metal on the guitar.
Ok, last thing here. How to wire the actual guitar signal. Wire the tip of the input jack to the middle prong on the volume potentiometer. The left prong on the potentiometer should have both the wire from the selector switch and a wire connecting to the left prong on the tone potentiometer. (I'm just describing the schematic shown above, basically.) Middle prong of the tone knob has a capacitor connecting to ground.
Ok, I think that's it as far as standard electronics in the telecaster.
If you need different schematics, this is the place to go: Guitar Electronics
I'll do part two of electronics if you'd like, going over advanced wirings with humbuckers and stuff like that. Email me for suggestions, or follow the blog and leave a comment!