4-Way light switches allow you to turn on or off a light or circuit from multiple 3-Way switches. The 4-Way switch acts as a median in between a series of 3-Way switches, allowing the 3-Way switches to use each other for the neutral and hot leads. 4-Way switches have four terminals that either connect directly across or diagonally. Installing a 4-way switch is relatively easy, but requires an already existing 3-way switch set-up to work properly.
Turn off the breaker for the circuit you are working on. If you do not know which breaker is the correct breaker for the circuit, you can turn off the master breaker, or consult a certified electrician.
Twist the bare copper ground wires from the 3-Way switches together. Leave a small tail at the end of the ground wire, so that you can loop it around the green grounding screw on the 4-Way switch. After you loop the wire around the screw, tighten the screw down on the wire.
Connect all of the white wires from the 3-Way switches together with a wire cap.
Connect the one red wire from one 3-Way switch to the brass screw on the right side of the 4-Way switch, and the black wire from the same switch to the brass screw on the opposite side. Each wire connects to the screw by looping it around the screw, and then tightening the screw down onto the wire.
Connect the red wire from the second 3-way switch to the black screw on the right side of the switch, and the black wire from the same 3-Way switch to the black screw on the opposite side of the switch.
Check your 4-Way switch's wiring diagram to ensure you are connecting the wires to the correct terminals.
Do not attempt to install a 4-Way switch with power to the circuit, or you may cause injury, severe shock, or death to yourself.