3 Way Switch Wiring. A 3 wire nm connects the traveler terminals of the first and second 3 way switch together. Connect the wire marked common to the black or dark colored screw.
Either way complete these five steps for 3 way light switch wiring. Add an electrical box for the second 3 way switch in the basement. Connect another black wire from the light to the original switch location.
Connect the two remaining traveler wires to the two brass or light colored.
Traveler wires are interchangeable on each switch. In the 1st diagram below a 2 wire nm cable supplies power from the panel to the first switch box. Add an electrical box for the second 3 way switch in the basement. Connect the two remaining traveler wires to the two brass or light colored.
