I'm trying to switch out an existing one way toggle switch for the Kasa HS200 smart switch. The left switch is the porch light I'm switching out. The right switch is the indoor foyer light. When I opened everything up I found the toggle switch has 2 black wires coming out of it. Then there's the bare ground wire (I believe came off when removing the switch). But theres that other wire on the side that's looped around the screw and connects to the foyer switch. I wasn't expecting to see this and am not sure what it's for or why the 2 switches that are unrelated are connected.

Edit: the right switch is part of a 3 way switch if that matters.

Edit 2: Added image with coloring to hopefully make the wiring more clear.

Also one ground wire runs through both switches and then up into the end of the green wire nut.

So what's the right way to wire this? Neutral into the red wire nut with the other neutrals, connect each black wire on the left toggle to the 2 black ones on the Kasa (does order matter?), and get the ground wrapped up in the green wire nut with the other grounds? What happens to that one extra black wire wrapped around the screw (and exposed there).

Thank you!

Wall Switch


Wiring with color

  • I duplicated my earlier post hopefully it is what you need.
    – Gil
    Commented Aug 11, 2021 at 1:13
  • @Gil I'm not entirely certain what you meant, but if you already answered a very similar question and simply copy/pasted your answer here, the best thing you can do is VtC this one as a duplicate of the other question instead of duplicating answers - that's the "SE way". If I've misunderstood your comment, then forgive me.
    – FreeMan
    Commented Aug 11, 2021 at 14:11
  • A 2-gang wall box with a Kasa smart switch on the left for a porch light and a 3-way switch on the right for a foyer ceiling light is exactly my situation too! diy.stackexchange.com/questions/290511/…
    – Ryan
    Commented Jan 6 at 21:44

3 Answers 3


That black wire, looped around one switch screw and continuing to the other switch (conveniently highlighted yellow in your last picture) is the "hot" power supply coming into the switch box and eventually makes its way back to your breaker box.

You can confirm this by carefully measuring with a multimeter when the power is on. Touching one probe to that black wire, and the other to the big bundle of white wires (with the red wire nut removed) should give you ±120v no matter what position either of the two switches is in.

Once you've confirmed this (or taken my word for it), TURN THE BREAKER OFF AGAIN. Then you'll want to disconnect the wire from that screw and cut it. It looks like you've got plenty of wire in the box (which is good!), so cut off all the exposed wire to get rid of the bent part. Strip back each of the newly cut ends to the length specified in your instructions (usually about 1/2").

You'll also need to remove the "backstab" wire (marked green in your overlay pic) from the back of the switch. Backstabs are notorious for failing over time, causing arcs and, potentially, house fires. Plus, you need to get this switch out of the box, so all the wires have to come off it. To remove that wire, you'll push a small screwdriver into the little slot next to the backstab hole and pull the wire out. You may have to twist & wiggle the wire a bit to get it out. Cut it if necessary.

You now have three wires to work with - 1 "green" and 2 "yellow" (they all have black insulation and all serve as "hot" wires, I'm just going with your overlay colors for ID purposes). You'll need a new wire nut of the same size as the red one that's already there. You'll add 1 of the black wires from your switch to that bundle (total of 4 wires) and tighten the wire nut down on the whole thing. Once you think you've got it good and tight, hold the nut then try to pull each wire out. This will ensure that they're all tightly held in place. If any come out, you had a loose connection that could have arced and caused a fire, so you need to try it again.

From there, continue to install per the instructions that came with your switch:

  • Remove the other backstabbed black wire (light blue) from that switch and connect it to the other black wire on your new switch.
  • Connect the green from the new switch to the bare ground wire bundle
  • Connect the white from the new switch to the white neutral wire bundle.

As noted in a comment, it may be that the hot power coming into the box could be the "orange" wire.

If that's the case:

  • Remove the "orange" wire from the right switch
  • Clip the "yellow" wire as directed above
  • Put both "yellow", the "green" and the "orange" under one wire nut with one of the black from the new switch
  • Put the now loose end of "yellow" back on the right switch (use the screw to properly fasten it, don't use the back stab).

Why is it that the left switch has two hots ("yellow" and "green") leading to it?

It doesn't. The "green" is an unswitched hot leading off somewhere else, possibly an outlet or another switch somewhere.

  • This is very thorough, thanks! Seems to make the most sense to me. But I'm curious, I assume in my overlay, the orange wire is hot and comes from the box, then the yellow wire picks that up from the right switch and brings it to the left switch and then goes off to a fixture. But then theres the green wire that also seems like its a hot wire coming from the box on a separate line. Why does the left switch get two separate hot wires?
    – Kevin
    Commented Aug 11, 2021 at 17:13
  • @Kevin see the updated answer
    – FreeMan
    Commented Aug 11, 2021 at 17:25
  • 1
    This makes so much more sense now, thank you! I installed as described above and everything is working.
    – Kevin
    Commented Aug 11, 2021 at 19:05
  • Hi, @FreeMan, thanks for your answer here. I have a similar question and was wondering if you could tell me whether I've done anything unsafe. Thanks! diy.stackexchange.com/questions/290511/…
    – Ryan
    Commented Jan 6 at 21:46

the three wires coonnected to the live side of the existing switch need to be connected together and connected to one of the black wires from the Kasa (perhapos use a wire nut)

The single black goes to the other black wire (another wire nut), the earth to the bare wires and the neutral to the big bunch of white wires.

be sure to use the correct size of wire nut in each case.


I posted this a few hours ago, maybe it can help you: "Here is my best guess on how to wire it, I do not have one so I can only look at sketches.

  1. Turn off the breaker
  2. Take pictures in case you have to put it back (done).
  3. Remove the plate and switch (done).
  4. Connect each of the two black wires from the switch to the live wires probably black
  5. Connect the Green wire to the ground line (bare or green wire)
  6. Connect the White wire to the neutral (white wire)
  7. Mount the new switch in the box
  8. Put the Wall plate on
  9. Turn the breaker on.
  10. You should be ready to go

You have part of it finished.

  • But then aren't I left with that other black wire that went around the screw on the left switch (and is stripped there). Does that just get electrical tape and pushed back into the wall not connecting to the new switch at all?
    – Kevin
    Commented Aug 11, 2021 at 1:17
  • The two black wires that are on the same terminal need to be connected together, it is most likely the feed to the other switch. I cannot clearly see what is there but it appears one stabs in the back the other goes under the screw, you should have no wires left. From what I can determine the two black wires coming out of the new switch form the switch portion and either can be power and output, the white is neutral as it needs power and the green is ground.
    – Gil
    Commented Aug 11, 2021 at 1:26
  • Two stab in the back and a third goes under the screw thats whats throwing me off. I realized the right switch is part of a 3 way switch if that helps.
    – Kevin
    Commented Aug 11, 2021 at 1:37
  • Apparently all three wires are connected, they need to remain that way. One of the new switches black wire goes to all the wires on one side of the switch, the other black goes to all of the wires on the other side of the switch. None left over. Be sure to kill the power first.
    – Gil
    Commented Aug 11, 2021 at 1:41
  • I added an image with color overlays to hopefully make it easier. So you're saying on my new photo the black wires with yellow and green overlay need to connect to each other and one of the blacks on the new switch. How do I connect an end of one wire to the middle of the other wire?
    – Kevin
    Commented Aug 11, 2021 at 2:02

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