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I have a pair of three way switches at the ends of my hallway that control a ceiling light and I'm working to replace them with new switches. I pulled out the old switch and put all the wires back on the same terminals on the new switch, but when I turned the breaker back on, neither switch was turning on the light. I did some research and figured it was probably caused by wiring the new switches incorrectly. The old switches didn't have any indication for which terminal was the common one (there was no black screw terminal or label or anything else) which I'm guessing contributed to me wiring it wrong. I've tried swapping some of the wires around to different terminals but so far I keep getting different results, with none of them being correct. The wiring coming into the boxes is a little confusing so I'm hoping to figure out the best way to find which wire goes where without having to go through trial and error. Here's the way the wiring currently looks:

Left switch:

There is one wire bundle coming in with a black, white, red, and ground. The ground wire was terminated to the box, and the black, white, and red wires went to the switch terminals.

image of light switch box with one wire bundle containing a black wire, white wire, red wire, and ground

Right switch:

There are two wire bundles coming in. One bundle has a black, white, red and ground and the other has a black, white, and ground. The two grounds are twisted together and terminate in the box. The two white wires are twisted together with a wire nut. The two black and one red wires went to the switch terminals.

image of light switch box with two wire bundles. One bundle contains a black wire, white wire, red wire, and ground. The other bundle contains a black wire, white wire, and ground.

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    The photos posted so far don't show any of the connections on the switches. So there's no info about the old connections, no info about the new connections, and if you want to know which wire goes where the only answer you'll get for sure is that they don't go where you put em if it aint working.
    – Robert Chapin
    Jul 31 at 17:38
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    Need to see the wire connections at the light. What's shown so far is incomplete.
    – Ecnerwal
    Jul 31 at 19:01

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Looks like you have a combination of a switch loop and a three way switch.

There's a nice diagram of the situation and a good explanation at hometips.com.

three-way switch loop

In this case the wiring colors in the image match the colors of the wires you're working with.

Current NEC rules now require the neutral to be present at all switch locations so this topology would not be accepted for new work. There are plenty of existing installations where it does exist, though.

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  • Thank you for this! I rewired the switches as shown in this diagram and now everything is working as expected.
    – BamSquid
    Jul 31 at 21:27

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