If you want a hands-free way to instantaneously mute your guitar, an on/off switch is a quick and easy way to do so. This pedal includes an LED that indicates when the pedal is on.
Because of the simplicity of this pedal, you can use a very small enclosure. These instructions will assume the enclosure is a 1290 size enclosure, which is roughly 2.25" x 4.25" x 1.25" (the size of MXR and Electro Harmonix Nano pedals). The Pedal Parts Plus website sells these enclosures, as well as all of the other parts you will need for this project. Effects Connection also has a good selection of parts.
You can order enclosures pre-drilled, but you might want to drill them yourself. The alignment isn't always perfect on the pre-drilled versions, and the holes aren't always where you'd like them to be. To drill your own, lay out all of the parts on top of the enclosure to ensure that they will fit (don't forget the battery). Use a marker to mark the centers of the holes (pencil does not show up well).
Drill a pilot hole for each of the markings on the enclosure. A 1/8" drill bit is a good size. Use a step bit (pictured) to drill the size you need for each component. You can get these in any hardware store. Make sure you clean out all of the metal shavings before installing any parts.
Install all of the parts as shown in the diagram, which is a bottom view of the pedal, as it appears with the back cover off.
Make sure that none of the parts are touching each other. Plug the cables in to make sure the contacts don't press against the switch or casing. Make sure the two LED legs are not touching.
Attach and solder the wires as shown in the diagram. The positive and negative legs (wires) can be determined by a few methods. The easiest to remember is that the shorter leg is negative. If you're using a used LED and the legs have already been clipped, the negative side has a flat edge on the plastic rim. Also, the negative side has a larger metal element inside the LED. It looks like a pennant. Before soldering the resistor leg to the switch, put a length of 1/8" or 3/16" shrink tubing over it. You can shrink it by running the soldering iron over it. Keep the iron moving steadily to avoid melting any spots in the tubing.
Use the stereo jack as the input and the mono jack as the output. The stereo has an extra contact that touches the sleeve of the 1/4" input. If you trace the wiring in the diagram, you can see that this will close the battery circuit when a cable is plugged in, but will open the circuit when there is no cable plugged in. That is why you should unplug the cable when the pedal is not in use---leaving it in will drain the battery even if you're not using the pedal. The lugs are located opposite their contacts. The lug for the input tip contact (the longer contact) is located directly across the ring from the tip contact. The lug for the input sleeve contact is across from the sleeve contact (the shorter contact). The ground lug is in the center. When in doubt, use a continuity tester to make sure you have the right lug.
Make sure the switch is wired correctly. Simply put, a DPDT (double pole, double throw) switch allows you to switch two signals at once. In this case, you're switching the guitar on and off by sending the signal to the lug connected to the output jack or to a lug on the switch that is not connected to anything. At the same time, you are opening or closing the LED circuit in a similar fashion, by sending the negative side of the LED to a lug connected to ground or to a lug that is not connected to anything.
Check your work. Use a continuity tester to make sure everything that is supposed to be connected is. You don't need the battery for this, but remember that you need to plug a cable into the input jack to complete the battery circuit.
Power up the pedal with the battery or AC Adapter (a 9V, center-negative 200 mA adapter will work fine). Plug your guitar into the input and your amp into the output and test in both the on and off positions. If the switch works for the sound, but not the light, check the battery first. Remember that the battery (and AC adapter) are only needed to power the LED. The switch will turn the guitar signal on or off, even without power. If that is fully charged, make sure you have the LED's polarity correct. Also, make sure you are using the correct resistor. Too low a value could burn out the LED immediately. Too high a value could prevent the LED from lighting. Between 1k-ohm and 2k-ohm should work. You should also check the wiring on the switch.
If the light works, but the sound doesn't switch on and off, check the wiring on the switch. If the wiring is correct, check the switch with a continuity tester to ensure the it works as it should.
Take your time. It is easy to make mistakes in simple projects by rushing.
Be careful with the soldering iron and keep the work area as tidy as possible. Look at the iron when you set it down to avoid inadvertently burning something. It's also a good idea to wear glasses, because solder has a tendency to spatter at times.