Testing a Three-Way Light Switch

A three-way light switch controls the light function at two different places.


A three-way light switch allows you to control a light at two different places. The switch is composed of a hot wire and two traveler wires that are hooked into another identical three-way switch through its own traveler wires. One or the other traveler wires is activated by flipping the switch up or down, and by doing this on each of the three-way light switches, you can turn the light off or on at either switch.

Check the Bulb and the Breaker

Check the bulb to make sure it is not burned out. Make sure the breaker supplying the three-way light switch has power. Check the breaker that supplies the switch confirm it is in the "on" position, then test the light switches. If the breaker is tripped, reset it and try the switch again. If the breaker continues to trip each time it is reset, there may be a short in the system, and a certified electrician must be called in to determine the problem.

Checking for Power

You can only test the switch safely when there is no electrical power present. Turn off the breaker that supplies the switch and check for power. An inexpensive voltage checker has two probes and a lightbulb. When the probes are touched onto the hot wire and one or the other traveler wire, the bulb should not light up. A better voltage tester is the noncontact type. It senses power at the switch without touching it. If the breaker to the switch is turned off and there is power, call in a certified electrician to troubleshoot the problem.

Testing for Continuity

Remove the switch cover from the wall once you have determined there is no power going to the switch, and pull it out of the wall, leaving all the wiring intact. Test the switch for continuity with a continuity tester. Attach the alligator clip to the common terminal, which is supplied by a black wire. Touch the probe from the continuity tester to one traveler terminal and flip the switch up and down. In one position, the probe lights up. Touch the probe to the other traveler terminal and flip the switch the other way. The probe lights up. If the probe lights up each time the switch is flipped up or down, or if the probe does not light up at all when the switch is flipped in either direction, the switch is faulty and must be replaced.

Lightbulb Socket

Since three-way switches control the flow of electricity to a light, power must flow through the lightbulb socket. If the switches that control the light show continuity, and the lightbulb is known to be good, test the socket. Use a continuity tester and make sure the power is off to the lightbulb circuit. Screw in a known working incandescent lightbulb and test the continuity between the terminals. Clip the alligator clip onto one socket terminal and touch the probe tip to the other socket terminal. If the socket is good, the probe lights up. If the probe does not light up, the socket is bad and must be replaced.

About the Author


Photo Credits

  • Jupiterimages/Comstock/Getty Images
Suggest a Correction