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I've seen other similar questions (How to trace mystery switches), but I have some more details:

  • This is in a master bedroom
  • There is a 2 gang box right near the inside of the door - one switch (purple wire and yellow wire) controls the overhead light. The other switch (purple wire and orange wire) is the mystery switch.
  • There are no switched outlets (I tried with a lamp)
  • There are no outdoor lights that I can notice (as suggested in the other answer)
  • I bought a Fluke Pro3000, turned off the power (purple was power anyway), hooked the red alligator clip on the toner to the orange wire, and tried sweeping the wall with the probe, but it was inconclusive at best
  • The pipe the orange wire enters from the box goes up

Any new guesses or suggestions of other experiments to do?

David Doria
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  • Questions: where in the world are you? Is this a house, and do you have an attic? (Side q: is there a fan in the attic?) If there's an attic, did you try the toner there? Did you use the toner at the panel? – Aloysius Defenestrate Feb 12 '19 at 03:33
  • @AloysiusDefenestrate Chicago, IL. Yes, it's a house. There is an attic, and I went up there but there is a foot of insulation so I can't tell where to step let alone see any wires to tone. The only thing I know of in the attic is a furnace. In fact I got really excited because there was a box near the furnace with an orange wire (and red and white), but it didn't tone out. I know which circuit the switch is on (the same one for the overhead fan/light) - I assume that's what you'd be looking for at the panel? – David Doria Feb 12 '19 at 03:37
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    Chicago has a reputation for running wire in conduit, which makes toners tough. I'd still try and wander around the attic with the toner wand. (Gloves, mask, and crawl from joist to joist -- they're usually 16-24 inches apart.) There's always the possibility that in the past there was a ceiling fan with separate circuits for light and fan... have you opened the light fixture? – Aloysius Defenestrate Feb 12 '19 at 03:43
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    Did you try both sockets in each outlet? Some outlets are split with separate control of each socket. I work a lot in conduit and think the conduit is *great* news. You can shove a fishing tape down the hole and get a sense of which way it's going, then open up boxes in that general direction. – Harper - Reinstate Monica Feb 12 '19 at 04:57
  • @Harper -- just a thought, but could he try injecting the toner signal onto the conduit itself? Or would that not work? – ThreePhaseEel Feb 12 '19 at 05:09
  • One of my rental houses has a switch by the door of the master bedroom that switches on 4 outdoor flood lights. Oddly originally it was the only control for those lights. – Tyson Feb 12 '19 at 12:17
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    @AloysiusDefenestrate You know, I have NOT opened the light fixture, but in hindsight that sounds like a pretty obvious thing to check. There is a fan + light where the fan is controlled by a remote, so perhaps it's not original and there used to be a fan that this switch controlled. I'll look tonight and report back. – David Doria Feb 12 '19 at 12:56
  • @ThreePhaseEel - I think I accidentally tried that (the manual said to "ground" the black lead on the toner so I connected it to the box while using red on the wire). In my testing with a free cable, it seemed like the black lead and red lead both did the same thing on the wire, so I think it would have toned the conduit already. – David Doria Feb 12 '19 at 12:56
  • @ThreePhaseEel *maybe*, that could be a good idea. Or inject it on the wire, and check at junction boxes, as most things that fit into junction boxes are not a faraday cage. – Harper - Reinstate Monica Feb 12 '19 at 19:15
  • Ok guys, I DID find an orange wire, not connected to anything, in the fan box! That's GOT to be it, but my toner STILL doesn't agree, even when I touch it directly to the wire... I've only tried this thing with very short wires, so the toner is still "in range" of the emitter - I'll have to try it on a longer wire outside the wall (so I know it's the same wire) and see if I'm doing anything wrong (though it seems pretty fool proof...). – David Doria Feb 13 '19 at 00:52
  • I used a continuity checker (with a long wire) and the orange wire in the fan box is indeed the orange wire in the mystery switch. So I guess I can close this question (thanks @AloysiusDefenestrate !) but now I'm super confused about why the toner won't tell me that's the same wire!? I tried out the toner on a separate 10' wire (in flexible conduit, even) and it worked exactly as I would have expected (the whole conduit as well as the exposed wires on the other end very clearly sounded the toner. – David Doria Feb 13 '19 at 03:07
  • I had been looking for this cable with the breaker to the room ON, because I knew the orange wire I was testing was not energized. I turned the breaker off and then my toner worked (found the orange cable). I was about to walk away happy with myself that I learned that a toner doesn't work on wires that are running next to other energized wires, but then I turned the circuit back on and tried again and IT WORKED?! I'm so confused about why it didn't work yesterday but is now working today, but I guess I'm back to "toners do what I thought they should", so I'm going to stop the madness haha. – David Doria Feb 14 '19 at 02:00
  • Happy you sorted it out. As to the toner, I'm sometimes mystified by what mine (same as yours) does and doesn't do... – Aloysius Defenestrate Feb 14 '19 at 03:43

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