• This Old House host Kevin O'Connor gets pro tips for finding—and replacing—a faulty three-way light switch

    Steps:

    1 Start by turning off the power to the circuit you'll be working on at the main electrical panel.
    2 Test the switches with a voltage tester to ensure the power is off.
    3 Remove the cover plate from the switch box with a slotted screwdriver.
    4 Unscrew the three-way switch you suspect isn't operating properly from the box.
    5 Before disconnecting the switch wires, label each wire for easy reattachment later, and mark the "hot" white wire with a black marker.
    6 Remove the suspect switch from the box and use a continuity tester to test its operation. If you find that current is allowed to pass through the switch, regardless of the position of the on/off toggle, then replace the old switch with a new three-way switch.
    7 After tightening the wire connections to the new switch, wrap electrical tape around the switch.
    8 Screw the switch to the electrical box, and replace the cover plate.
    9 Test the new switch by flipping on and off the three-way switches at each end of the circuit.
    • 15 to 30 minutes, depending on how many switches you need to test and replace
    • About $2 to $4 per new switch
    • Difficulty: Moderate
      requires basic understanding of electrical lighting system
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      Tools List

      • Phillips screwdriver
        Phillips and slotted screwdrivers, used to remove and replace cover plate and switch, and to tighten wire connections
      • electrical tester
        Voltage tester, for ensuring the power is off at the switch box
      • continuity tester
        Continuity tester, for testing operation of existing three-way switch
      • black marker
        Black marker, for marking white-wire lead on three-way switch

      Shopping List

      1. Three-way switch, used to replace an existing faulty three-way switch

      2. Electrical tape, for wrapping around wire connections on new switch