Troubleshooting three-way switches can be confusing if you're not familiar with them. They're used wherever you need to turn a light on or off from more than one location, like hallway and stairway lights. Three-way switches work in pairs. A three-way switch has three screw connections, not counting the grounding screw. There's one dark or brass "common" screw and two lighter or silver matching colored "traveler" screws. It's known as a single pole double throw switch in technical terms. Meaning they switch one common screw between two possible switch positions, the two traveler screws. The common wire on each switch is the power wire feeding the first switch, or the switched power wire that controls the light, from the second switch. The travelers are the two wires that connect the two switches, and possible switch positions, together.
Instructions
1. Turn off the breaker controlling the power to the light switches you're working on. With your straight tipped screwdriver, remove the covers of the two switches that control the lights. Remove the screws holding the switches into the electrical boxes and pull the switches out of the box so that all of the wires are visible.
2. Inspect inside one of the boxes. Follow the wires connected to the light colored "traveler" screws on the three-way switch to where they enter the electrical box. They should be the red and black wires that are in the same insulated sheath. These two wires travel between the two switches, one wire for each switch position, or "traveler" screw.
3. Follow the black wire connected to the dark or brass "common" screw on the three-way switch. Confirm that it's either attached to other black wires in the box, or enters the box with only a white and bare wire in the same sheath.
4. Repeat Steps 2 and 3 for the second three-way switch box. Disconnect and replace any wires that are not connected to their appropriate screws according to the descriptions in the steps. There are two black wires connected to three-way switches and confusing the two is the most common error.
5. Replace the switches into the electrical boxes and reinstall the cover plates. Turn on the breaker and test the switches. Whichever switch you use, the light should change states. Test each switch in each position to confirm they are turning the light on and off from either location.
Tags: three-way switch, black wires, common screw, each switch, light from