At times, a three prong switch is indispensable, especially when customising a car. Being able to quickly change modes between several electronic accessories is an ideal job for a this switch. Three prong switches are not as commonly used as two prong ones, but when the application calls for this design, they are easy to understand and not difficult to wire.
Drill a 1/2-inch hole and mount the three-pole, toggle switch in a convenient location. The switch function is "Off" when the lever is in the centre position, and "On" in either up or down. Tighten the switch mounting retainer with a wrench.
Route a positive wire from the switch to the fuse box. Use a fuse tap and connect the wire to a source that provides either power at all times or power with the key on, depending on your application. Locate this source with a test light. Strip 1/4-inch of insulation off of the wire on both ends with wire strippers and crimp a terminal on the exposed copper. Plug the power wire into the fuse tap and the centre pole of the switch.
Prepare two wires and route them from the switch to the two objects that are being installed. Plug the wires to the two outer poles of the switch and connect them to the power feed wires of the objects. Once the objects have ground wiring installed, the switch will control their on and off function.
Although this switch is designed to control two objects, it will only control on at a time. When one is on, the other is off. For example, stereo speakers normally play inside the car, but by using this switch, the stereo can power outside speakers for a beach outing. This way the stereo amplifier is not overstressed by trying to power too many speakers at one time.