People seem to love killswitches, just look at Buckethead and Tom Morello, and a lot of people want to put them into their guitars. I have nothing against this, all the more power to you. The problem I see is with solutions that still produce an audible hum when the killswitch is engaged. This is because a lot of solutions short-circuit the guitar or cable, rather than actually killing the signal-path.

You see, no matter how much you payed for your guitar cables, there will still be some level of hum produced by your rig, especially with an extensive pedal-board, or with distortion effects like fuzz-boxes so long as the circuit that is your rig is closed. In this instructable, I will show you how to add a noise-free killswitch to any guitar with a 1/4 inch output jack.

Step 1: Parts

You will need:

-- A guitar, obviously.
-- A pushbutton normally closed momentary switch. It is very, very, important that the switch be normally closed, check the package carefully before you buy your switch.
-- A soldering iron.
-- Solder.
-- Heat-shrink tubing (or electrical tape in a pinch) to make everything all nice and pretty, and to prevent accidental short-circuits.
-- Screwdrivers that can open up your guitar.
-- Wire cutters and wire strippers.
-- A drill with an appropriately-sized bit. Check the packaging for your switch to see if a mounting-hole diameter is listed, since this will help a lot. If you can't find a listed size, err towards a smaller hole, since you can make holes bigger, but not smaller.
-- You may also need a bit of extra wire if there isn't enough slack, a foot of stranded 20 AWG copper wire should be more than enough.

Step 2: Prep-work

Before you can install your killswitch, you are going to have to get at the guts of your guitar, specifically you will need to get at the wires that go to your guitar's output jack. Find the wire that connects to the sleeve of the plug, in most guitars this wire will be black. Trace this wire back to the guitar's volume pot (or wherever the wires finally come together to become a single pair), but don't cut the wire yet.

Now you're going to have to figure out where you want to put the switch. Unless you're willing to do a lot of extra work, you'll be limited in placement options by where the guitar's control-cavity is. Once you've determined where you want to place the switch, carefully mark the position and then drill a mounting-hole for the switch. If you're drilling through the body of your guitar, drill very carefully through the front of the guitar so that if there is any accidental splintering, it will be out of sight. To minimize the risk of splintering, you should press very gently while running the drill at a high speed.

Step 3: Installation

Now comes the time to cut that wire that you traced back at the beginning of the previous step. Before cutting the wire, make sure that there is enough of the wire to go from the volume pot (or wherever) to the switch and then to the output jack; if there isn't enough wire for this, you'll have to splice some in. Whichever way it turns out, wire in the switch; if your switch needs to be installed in the guitar before connecting the wires, do so now and save yourself some time and effort. Also make sure, if you're using heat-shrink tubing, that it is in place before soldering your wires.

Make sure to insulate all your connections, and test them somehow before you close everything up, especially if you had to de-string your guitar in order to install the switch. The best way I have found to test your wiring is to plug your guitar into an amp, turn on the amp, and then stick some ferric object (like your screwdriver) onto your selected pickup, or if you did not have to remove your guitar's strings, pluck a string; if you don't get any sound make sure first that the volume is up on both the guitar and amp, and then that your selector-switch (if applicable) is set to the proper pickup. If you get sound, then you're golden, otherwise go back and check all your connections.