I have two 3 way switches controlling one light. Sometimes when the light is on neither switch will turn off the light but one of the switches will turn light off if switch is placed half way between on and off. Would this be the switch that is wired wrong or do I have to take off the plates and look at wiring of both ?

In both pics the left most switch are the problem ones. Strange thing is they both looked wired correct. It appears the travelers red and black are both on bottom.

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  • 1
    Yes, and shoot us some photos of the insides of the boxes. Pay close attention to how wires are grouped into cables in the back of the boxes. Don't unhook the switches. Aug 4, 2018 at 1:28
  • Okay will do tomorrow morning when I have some sunlight to work with !
    – Steviekm3
    Aug 4, 2018 at 2:00
  • Ok added some pics. It is strange as the wiring looks good. This is builder that wired home.
    – Steviekm3
    Aug 4, 2018 at 14:38

2 Answers 2


Get an electrician with an insulation resistance tester in to check this out further

Since both 3 way switches appear to be wired correctly, the one cause left remaining in the wiring system is a short between the two traveler wires themselves. To find this, I would have an electrician come in and unhook both traveler wires at both ends, then measure between them with an insulation resistance tester (often called a "megger"). From there, it would be a matter of chasing down any shorts found, and replacing either the entire cable or patching in a section of cable using NM splice kits to repair the situation.

If it isn't that, then I'd have the switches themselves checked, although that's less likely than an errant staple or nail causing a short.

  • 1
    Or a bad switch, perhaps. Aug 4, 2018 at 16:13
  • @Harper -- yeah, the switch would have to be shorted from throw to throw internally (not just welded in a position or smth like that), though...I'd consider the bad cable much more likely Aug 4, 2018 at 16:46
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    You are correct, there is a short. I disconnected both switches and then connected hot wire to the black traveler wire in the box that gets power. Then turned on power in circuit box, and tested. Both the black and red traveler wires became hot. It is strange as House was built in 2012 and 2 rooms have this problem. I would think builder would have tested this.
    – Steviekm3
    Aug 4, 2018 at 18:45
  • 1
    @Steviekm3 Builder's (don't test more than they need to. Turns on/off once correctly done. That is for the same reason they use backstab connections any other shortcuts they can - time = money. Time is money for the rest of us too, but the builders are looking at how many houses they can get wired in a day as that directly affects their bottom line. Save $100 is not such a big deal for an individual. But for a builder they look at $100 x 100 houses = $10,000 == vacation time! Jan 1, 2019 at 15:37

Bottom photo is where power enters the 3 way, travelers go to top photo. All is OK in bottom 3 way wiring.

On the top photo common should go to the load (light). But the black traveler goes to the "common" lug of the 3 way switch - wrong!

On top photo, the 2 black wires need to swap locations.

  • Hello, and welcome to Home Improvement. Thanks for the answer, but signature lines and the like should be put into your profile. Jan 1, 2019 at 16:47

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