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How to Troubleshoot Three-Way Switches

How to Test a 3-Way Switch

  1. Turn off power to the switches at the circuit breaker and using a tester, make sure power is off. Pull the two 3-way switches out from their switch boxes so you can access the switch terminals. The wire connections do not have to be removed. Find Multimeters
  2. Using a continuity tester or the continuity setting on a multimeter, check the continuity between the common (black) terminal and each of the traveler terminals (brass colored) of each 3-way switch.
  3. There should be continuity between the common terminal and only one of the traveler terminals. After toggling the switch, there should be continuity between the common terminal and only the other traveler terminal.

When a 3-way switch fails, there will usually be no continuity between the common terminal and one (sometimes both) traveler terminals of one of the 3-way switches.

How to Locate a Bad 3-Way Switch

Usually when a 3-way switch fails, lights can be toggled on and off at one switch, but not the other. If one of the two 3-way switches toggles the light(s) on and off, the other 3-way switch has probably failed. Follow these steps to find which switch is bad.

  1. Toggle each switch until the light comes on. Toggle one switch to see if it turns the light on and off. If it does, it is a good switch. Leave the light on.
  2. Toggle the other switch to see if it turns the light on and off. If it does, it is a good switch and the other is bad.

One of these switches will not turn the light on and off (while the light is on) and that is the bad switch.

Once you identify the bad switch, follow the steps below to verify it is bad and needs to be replaced.

Note: This article only applies to conventional 3-way switch wiring.

Switches are spring loaded to minimize arcing and prolong their life. However, a very small amount of arcing is present when a switch is toggled. A bad switch may not fail completely, burned contacts may cause intermittent failure. Keep this in mind when troubleshooting switches. Intermittent failure could make troubleshooting difficult, especially with 3 and 4-way switches. If one 3-way switch needs to be replaced, the other one should be replaced too.

Black common wire is usually wrapped around the two traveler wires on a 3-way switch.

How to Test and Replace a 3-Way Switch Video

How to Test and Replace a 3-Way Switch VideoCommon wire wrapped around traveler wires
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Troubleshoot 3-Way Switches

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3-Way Toggle Switch Animation

3-Way Toggle Switch Animation

When the switch toggle is in one position, you should get continuity between the common and one traveler terminal

3-way switch toggle 1 Arrow left up short Arrow left down short 3-way switch toggle 2 Arrow left down short Arrow left up short

Toggle

Decora

3-way switch decora 1 Arrow right up short 3-way switch decora 2 Arrow left down short Arrow right down short Arrow left up short

When the switch toggle is in the other position, you should get continuity between the common and the other traveler terminal

Decora

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