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Like many others here, I am looking to replace a 3-way switch with a "smart switch" that requires neutral. As I inspect my wiring (home built in 2009) I note that I can't tell the difference between two wiring schematics by looking at the switches themselves.

In looking up diagrams of these to add to this post, neither of these arrangements seems very common. I would add pictures of my switch boxes but they're both multi-switch boxes, one of which is very full and hard to track in-person, I can only imagine it'd be more confusing from photos. The other is extremely simple, 14/3 connected straightforwardly. I narrowed down my situation to 2 possibilities based on what I see.

Can a voltmeter or non-contact voltage tester help determine which of these I have? Or is there another way to tell without opening up the lights themselves? I found diagrams with 2 lights but I actually have 4 connected somehow to these 2 3-way switches.

Possibility 1:

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Possibility 2:

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EDIT: Adding photos of switch wiring.

Switch 2, which I found straightforward:

enter image description here

And here are two of Switch 1 which looked straightforward at first, but eventually I saw the black wire from the 14/3 does NOT go directly to the switch, it's coming from the 14/2 I marked in green (mspaint). I lose track of the black from 14/3 and the white from 14/2 as they go off to the left side of the box. Short of stretching all the nutted wire bundles out of the box, I'm convinced they're connected to each other (unless that doesn't make sense). I don't know that I can get all the wire bundles crammed back in the box as neatly as they are now so I've tried not to move them so far.

Switch 1:

enter image description here

enter image description here

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  • Can you add photos of the insides of the switch boxes anyway? Also, have you tried looking inside the light fixture boxes for clues? – ThreePhaseEel Oct 13 '20 at 23:55
  • Use colored electrical tape to mark the travelers yellow. You'll thank me later. The 2 travelers are the ones going onto the brass/ yellow screws. – Harper - Reinstate Monica Oct 14 '20 at 1:45
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    Possibility 1 was drawn by a drunk skunk. It will not work. – Harper - Reinstate Monica Oct 14 '20 at 1:50
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    DO NOT REMOVE WIRE NUTS! At least not until you understand what's going on or, at an absolute minimum have marked all your wires so you know which ones went where! This place is full of "I pulled all the nuts off my wiring and now I have no idea how to put it back together" questions – FreeMan Oct 14 '20 at 13:27
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    @FreeMan Good point, I facepalm when I see those posts too. I didn't mean remove them, I meant pull the whole bundle out of the box so I can see better. Regardless, I'd rather not do either unless necessary because they're pretty neatly/tightly crammed. – Fredric Shope Oct 14 '20 at 13:31
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Actually since there are no white wires on the 3-ways, this gets simple.

The black and red wires that DO go to the 3-ways are part of cables. Note which cables they are. It matters.

Almost certainly, two cables are involved, and the 2 white wires in those cables are connected to each other.

As long as that's so, you can add the smart switch's white wire to those two white wires (might be more than 2).

Do keep in mind that with smart switches, often, the smart switch's design will dictate where it must go. So don't just go "Imma puttin it there" and try to force it to work. Actually read the instructions and think about what you're doing.

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  • I'm not sure I follow. I can't tell from looking at the switches whether I have power coming into switch 1 or if that 14/2 cable connects to the lights (with power connected at the lights). As @manassehkatz commented, it could be power -> lights -> switches or power -> switches -> lights. If it's power -> switches I should have neutral on that white from 14/2, if it's not then I wouldn't - right? – Fredric Shope Oct 14 '20 at 18:52
  • @fred on any “switch on the end” scenario, there would have to be a white wire (re-marked to be a hot) going to a switch. There is none, therefore the switches are in the middle. – Harper - Reinstate Monica Oct 14 '20 at 20:55
  • Both 3-ways have a black-painted white wire in the 14/3 cable going directly to the switch (the red and white-traveler switch sides on each switch - I don't think that matters). That's why I dug up the two diagrams I posted. I still don't know what the wiring looks like at the lights themselves; I was hoping there's a way to test from the easily-accessible switches and not have to open 4 light fixtures up high outside. – Fredric Shope Oct 14 '20 at 21:17
  • @FredShope That's a heck of a thorough painting job. Can't tell it's not a black. Following all 3 wires on the switch, are all 3 going into the same cable? On both switches? – Harper - Reinstate Monica Oct 14 '20 at 23:51
  • @FredShope -- are you sure that you're seeing a white wire that was painted black, not a black wire that was painted (or plastered!!!) white? – ThreePhaseEel Oct 15 '20 at 1:52

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