Wire a 3-Way Switch (Two Switches, One Light)

Understand the job: a pair of 3-way switches controls one light from two places. Each switch has one COMMON terminal (dark or black screw), two TRAVELER terminals (brass, interchangeable with each other), and a green ground screw.

Turn off the breaker feeding the light, then verify the wires are dead with a non-contact tester and confirm with a meter before touching anything.

Identify your cables. In the most common layout, power (a 2-wire cable) enters the first switch box, a 3-wire cable runs between the two switch boxes as the travelers, and a 2-wire switch leg leaves the second switch to the light. If power instead enters the light box (a dead-end or California 3-way), the 3-wire cable still carries the travelers between switches.

At switch 1: connect the incoming hot (black from the panel) to the COMMON terminal. Connect the two traveler conductors of the 3-wire cable (usually black and red) to the two brass traveler terminals — either order is fine. Splice the neutral (white) through to the light; it never lands on the switch.

At switch 2: connect the same two traveler conductors to the two brass traveler terminals, and connect the switch leg going to the light to the COMMON terminal.

Bond the grounds: connect the bare or green equipment ground to the green screw on each switch and to the box if it is metal.

At the light: switch leg (hot) to the fixture hot, neutral to the fixture neutral, ground to ground. Mark any white conductor used as a hot with black or red tape at both ends.

Fold the conductors neatly into the boxes, screw in the switches, and install the cover plates.

Restore power and test: the light must turn on and off from either switch, in every combination of positions. If it only works from one switch, a common and a traveler are swapped — kill the power and move the wire from the brass terminal to the dark COMMON terminal (or the reverse) at the switch that fails.