Adding a coil tap switch onto the humbucker bridge pickup of an electric guitar is designed to short out one coil of the humbucker, thus giving the guitar the tone of a guitar with a single coil. Although most guitars do not come with this option preinstalled, if the humbucker in your guitar has four coloured wires and a bare wire protruding from the wiring harness you can convert your standard humbucker into one capable of coil tapping.
Locate the electronics cover plate on the back of the guitar and remove the screws that hold the plate onto the guitar with a screwdriver. Lift the cover plate off the guitar to expose the electronics.
Locate the place where you want to mount the coil tap switch. It should be in a location that is easy to reach with the hand you "pick" the guitar strings with and it must be out of the way of the other electronics.
Place blue painter's tape on the face of the guitar where the switch will be and mark the location where you want to add the switch.
Drill the hole for the mounting switch using a hand drill. Remove the tape once you have drilled the hole.
Mount the coil tap switch to the guitar using a small wrench. The toggle portion of the switch should stick though the top of the guitar and the electronic solder points should be inside of the electronic cavity.
Locate the two wires that were not wired into the guitar's electronic circuit. These wires are twisted and taped together by the manufacturer. Remove the tape and separate the wires from each other.
Solder both wires to the centre-soldering lug of the coil tap switch.
Solder a wire to the soldering lug that is to the right of the centre-soldering lug and solder the other end of that wire to the back of a potentiometer.
The size of the drill bit needed and the size of the wrench depend on the size of coil tap switch you choose to use. A simple SPST (Single Pole Single Throw) switch will work for basic coil tapping. If you do not want to drill a hole into your guitar you can use a push/pull potentiometer in place of a switch. Pulling up on the knob activates the switch.