Three-way switches work together to operate a light from two different locations. This is most convenient in a long hallway or at the top and bottom of the staircase. The Natural Handyman states that numerous homes across the United States have miswired three-way circuits that have caused inconveniences and safety hazards. Three-way switches only take a few minutes to wire correctly. You can hook up a light switch with two black wires and one red wire without a wiring diagram.
Turn the power off at the main breaker panel that supplies electricity to the switch circuit by turning off the breaker.
Locate the common terminals on your three-way switch. A three-way switch has two common wire terminals, usually dark in colour. On the back of the three-way switch, you will find them labelled as COM. These two terminals could be on the same side of the switch or on opposite sides of the switch.
Locate the black wires inside your light switch box. The black wires feed the power to the light fixture. Wrap a black wire around one common terminal and tighten the terminal to hold the wire onto the switch. Place the remaining black wire onto the remaining common terminal and tighten it also.
Locate the red wire inside the switch box. The red wire or traveller wire runs between the switches in the three-way circuit. No electrical power runs through the red wire, it simply connects the two switches together. Wrap the red wire around the remaining terminal on the three-way switch and tighten it to hold the wire in place.
Push all the wires into the electrical box and attach the three-way switch to the box at the top and the bottom using screws provided with the switch. Cover the switch with a single gang switch cover plate.
Turn the power back on to the circuit by turning the breaker on at the main electrical panel.
Make sure the electricity is off to the area that you are working in to avoid electrical shock.