How do I wire a three-way switch if there is 1 red and 2 black wires?

Answer by  Scotti (61)

First, you need to determine which wire is live. Almost definately it will be one of the blacks. Use a set of testers/tracer. Once you know which leg is hot, that will be your common wire, which will go on the black common screw. The other black and red wires, are your travelers, they go on the other two screws.

Answer by  joemason (83)

The red should be the common and the blacks should be the travelers. On the switch you have one screw that is labeled common that is where to attatch the red.