How to Wire a 3 Way Dimmer Switch - Ask-The-Electrician Wiring a Standard 3-Way Dimmer Switch. 3-Way Dimmer Switches typically come with the following pre-wired leads. Green wire: Attach to the bonded ground wire(s) in the switch box. Two Red wires: These wires attach to the "travelers" which are the pair of wires attached to the two screws at one end of the regular 3-way-switch. 3 Way Switch Wiring Diagram - Easy Take a closer look at a 3 way switch wiring diagram. Pick the diagram that is most like the scenario you are in and see if you can wire your switch! This might seem intimidating, but it does not have to be. With these diagrams below it will take the guess work out of wiring. Dimmer Switch Wiring - Electrical 101 In the diagram below, a 2-wire NM cable supplies power from the panel to the dimmer box. The black (line) wire connects to the common terminal of the 3-way dimmer. A 3-wire NM connects the travelers of the dimmer to the travelers of the 3-way switch. Traveler wires are interchangeable on each switch.