I am in the process of upgrading an old light switch in a bedroom. Coming out of the wall is a white wire, ground, two black wires, and a red wire.

What is bizarre, or something I'm not understanding, is the red wire - it appears to have something to do with the lights in the hallway, because depending on which set of black wires it gets paired to, the bedroom light switch either controls both the bedroom and hallway lights (rendering the hallway light switch inoperable), or the hallway lights only.

In addition, when I was starting the project and getting all the wires untangled there is now an additional black wire, unconnected to anything on either side.

Can someone assist? I would be glad to provide more info or pictures.

The light switch I'm trying to install in the bedroom is the Kasa HS200, the light switch in the hallway, like the one replaced in the bedroom, is some generic flip on/off.

Current wiring, having the red wire by itself results in the bedroom switch controlling the hallway only (and not ceiling lights)

  • Show us the pictures you took before disconnecting anything.
    – JACK
    Oct 29, 2022 at 1:11
  • I was dumb and did not take any pictures before disconnecting. Oct 29, 2022 at 1:14
  • just to clarify, you no longer want the two switches to work together
    – Traveler
    Oct 29, 2022 at 2:14
  • Yeah, each room has its own switch that should control its own lights. Oct 29, 2022 at 2:45
  • OK, then you need to disconnect the 3 way switch whirring, remove the two trawlers connecting the two switches
    – Traveler
    Oct 29, 2022 at 2:57

2 Answers 2

  • /2 cable is BLACK, WHITE and bare.
  • /3 cable is BLACK, WHITE, RED and bare.

Cables come in those 2 styles, and that's what the wire colors mean. (well, bare is ground and if neutral is present, it's white). There's no other meaning to it.

Let me say again. Black and colored wires have no meaning/role defined by color. That's simply how cables are made.

You've been assuming the 2 blacks from the switch must match 2 blacks from the wall, and the colors don't have that much meaning.

From your circuit, we know two of the wires are "always-hot" - one comes from supply and the other goes onward to other switches. One wire is "switched-hot" for the bedroom lamp. Since you've tried every other combination, I suspect both blacks are "always-hot", and the red is "switched-hot".

Both blacks go together to the Line/Supply wire on the switch, which is black.

The solo red goes to the Load/Lamp wire on the switch, which is black.

Read the labeling and instructions for how to distinguish which wire is which on the switch. Sometimes it doesn't matter.

  • Thank you for the info. What's clear to me is I went into this without doing the requisite research and am in way over my head. I will absolutely take what you said and go from there. Oct 30, 2022 at 12:04

The red wire should be tied into whatever black wire provides the "hot" to that switch box. You will need to determine which black that is. The lead designated to provide power into the new switch is tied to the same red and black. The black that is then remaining is the lead to the lights in the bedroom to be controlled by the switch you are installing. That will correct your problem.

  • Appreciate the response and info. I tried both black wires - one is connected to red and the other black wire is connected with the two black wires from the Kasa light switch. Neither one seems to do what I want. There is however another black wire but it as far as I could tell was not connected to anything. Or maybe it was but I don't think I pulled anything so hard as to yank it out of the wall. Oct 29, 2022 at 3:09
  • what you are describing is not shown in your pic. In your pic the red is connected to nothing. For now forget the Kasa switch and get the hall wiring back to what it should be. Then you can concentrate on just the wires to the bedroom lights which were only the wires on the original switch.
    – RMDman
    Oct 29, 2022 at 11:57
  • I have tried combining the red with each set of black wires as well, with no success. Either it does not control the bedroom lights or it only controls the hallway Oct 29, 2022 at 13:11

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