How To Troubleshoot A Malfunctioned Three-Way Switch

You may think that three-way switches control three different lights, but that's not how they work. In spite of the name, a three-way light switch controls the power in two different locations, as a four-way switch controls the light from three locations.

A standard light switch has two individual terminals, while the three-way switch has three terminals with one terminal connected to a second or third terminal. If the light switch is giving you trouble, here are some ways to troubleshoot the issue.

Find the Malfunctioned Switch

To test the switch, you need a multimeter, a Phillips screwdriver, and a flat-blade screwdriver. Sometimes, only one switch will fail on a three-way switch, so flip each switch to see if it turns on the lights. 

After you find the faulty switch, take the control panel off the breaker box with a screwdriver, and look for tripped breakers. You can identify tripped breakers by noting their position, which moves the opposite from the other breakers.

Move the tripped breaker back to its original position, and try the switch again. If that didn't help, proceed to shut off the power to the room.

Inspect Wiring Connections for Reverse Polarity

When the switch fails, the wiring could be improperly installed, usually from someone else tampering with it. Run a multimeter over the switch to ensure no current exists.

Use the screwdriver to detach the switch screws, and lay them aside. Check for loose or charred wiring, and that the wires are secured to the screw terminals in a pigtail.

Inspect the wires for reverse polarity, or backward wiring, of black or red (hot wires) and white (neutral) wires, which can create electrical hazards, if it is ignored. Press the tip of a small flat-blade screwdriver into the slots to detach them, and connect them to the correct screw terminal. Hot wires connect to brass terminals, and white wires connect to silver terminals. Reattach the plate, and try the switch again.

Test Wires for Continuity

If the wires are connected properly, and the switch still doesn't work, test for continuity. Loosen the screws on the switch, and pull it from the wall with the wires still connected. 

Hook the probe clip to the black hot wire. Touch a probe to a travel wire (located on each side of the switch), and turn the light switch on and off, which should light the probe in one position. 

Repeat the test on the other travel wire, reversing the direction of the switch. If the wires light the probe with each flip of the switch, or they don't light at all, replace the switch, or hire an electrician to replace it. Contact an electrical service, like Richardson Charles E Electric, for more help.