3-Way Switch Installations – The Power Source from the Fixture

In a three-way switch rough-in, there are a number of different ways that the circuit can be run in order to get the results you’re looking for. However, when you’re trying to install a three-way switch circuit in a finished room; your options are not as flexible. In a finished room, your choices are dictated by where the power feed is coming into the room. Here is how to wire a three-way switch circuit when the power feed is coming through the light fixture.

So, before you begin, let’s look at what you currently have in the room – a light fixture and a single-pole switch. There is already a line running from the switch to the fixture, so keep in mind that in order to install a three-way switch, you will have to run another line from the existing switch box to the location of the second switch. This new line will have to be a length of 3-wire NM cable (black, white, red and ground wires).

Turn off the power to the circuit before you begin working on it.

Next, disconnect and remove the switch and light fixture.

Run the new cable from the existing switch box (switch #1) to the one you are installing for the second switch (switch #2).

Here are the instructions for wiring the switches, starting with the switch in the newly-installed box (switch #2):

Wiring Switch #2 

• Connect the ground wire to the ground screw on the switch.
• The BLACK wire in the box gets connected to the DARK colored screw on the switch.
• The WHITE wire gets connected to the screw directly underneath the black wire. Wrap electrical tape around the white wire to identify it as a current-carrying wire.
• The RED wire gets connected to the single screw on the other side of the switch.

Wiring Switch #1 – This one is a little more complicated, but just follow the directions and you’ll be fine.

• First, connect all of the ground wires and branch off with piece of ground wire to connect to the switch’s ground screw.
• Next, take the WHITE wire coming from the FIXTURE and connect it to the BLACK wire that is traveling to Switch #2 (again, wrap the white wire with black electrical tape).
• Take the BLACK wire coming from the fixture and connect it to the DARK colored screw on the three-way switch.
• Take the WHITE wire that is traveling to Switch #2, wrap it with electrical tape and connect it to the screw directly under the black wire.
• Take the RED wire that travels to Switch #2 and connect it to the single screw on the other side of the switch.

Wiring the Fixture

• Connect all of the ground wires together.
• Take the WHITE wire coming from the electrical panel feed and connect it to the neutral wire on the light fixture.
• Take the BLACK wire coming from the electrical panel feed and connect it to the WHITE wire that travels to Switch #1 (wrap the white wire with electrical tape to identify it as a hot line)
• Connect the fixture’s BLACK wire to the BLACK wire that is traveling to Switch #1.

Dave Donovan is a freelance copywriter living in Atco, N.J. An electrician for 15 years, an injury forced him to pursue his true passion - writing.