Ask This Old House host Kevin O'Connor helps a homeowner fix a faulty three-way switch. (See steps below.)
Steps for How to Repair a Three-Way Light Switch:
1. Turn off the electricity to the three-way light circuit at the main electrical panel.
2. Remove the cover plates from both three-way switches, then unscrew the switches from the electrical boxes.
3. Use a battery-powered continuity tester to determine which two wires in each box are the traveler wires.
4. Reinstall both three-way switches, making sure to connect the identified traveler wires to the appropriate traveler terminals on each switch.
5. Next, attach the common wire and ground wire to each switch.
6. Screw each switch back into the electrical boxes and reinstall the cover plates.
7. Turn the electricity back on and test the switches to ensure that each one can turn on and turn off the light.