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I'm aware that the WeMo light switch does not work as a 3-way switch, but I had purchased it before opening up the existing light switch plate and understanding the wiring I would work with.

Anyway, I removed the light switch plate and discovered what appears to be a 3-way switch. (I recently moved into this house with a whole bunch of sketchy wiring, and actually DO NOT know the location of another switch that controls that same set of exterior lights on my detached garage!) A red jumper cable is connected to the common terminal of the switch, and two black cables connect to the other terminals on the light switch. The box didn't exhibit any obvious sign of a separate (white) neutral cable.

On a lark, I decided to wire the WeMo as follows:

  • Red jumper cable to the expected white, neutral terminal on the WeMo,
  • Black cables to black terminals on the WeMo, and
  • Capped the green/ground terminal on the WeMo.

To my surprise, the WeMo had power and booted up. However, when I pressed the WeMo button to turn on the lights, none of the garage's exterior lights turned on. I swapped the black wires and encountered the same dead end, so I restored the old switch and can turn the garage's exterior lights on/off.

I'm certainly disappointed that I didn't successfully install the WeMo, but I'm also confused. If the WeMo had power, clearly I had both hot and neutral correctly wired to the WeMo. Assuming the WeMo isn't defective, why wasn't it actually acting as a switch? What are some theories on how these lights are actually wired?

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    If the WeMo does not work as a 3-way switch, yet you wired it as one, that is probably why it's not controlling your lights as expected. You need to figure out where your other unknown 3-way switch is and go from there
    – mjohns
    Jul 11, 2015 at 11:25

2 Answers 2

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I'm just thinking out loud here. It is hard to state anything with certainty in a situation like this where there is no guarantee of what somebody else did with the wiring a long time ago...so forgive me if this suggestion isn't even worth what you paid for it. ;)

From what you have said here, it sounds to me like that red wire makes its way back to the lights, and acts as the "hot" for the lights. Who knows where the lights are getting their neutral side connection. Doesn't really matter. Obviously it is getting there somehow.

So to make the lights light, your existing switch is getting "hot" from one of the two black wires, and is supplying that to the red wire.

So think of your red wire as the "hot out", and ONE OF the two black wires is your "hot in".

So you need to use a meter to see which one of the two black wires is your "hot in", and treat it that way and cap off the other black. Then use your red wire as the "hot out".

Again, this is just me thinking out loud about what I would try. I take no responsibility for any bad stuff that might result from it. All possible disclaimers apply. ;)

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  • BTW, is there no obvious ground wire in there? Is it a metal box? Maybe the box is grounded. I'm thinking if it is you should hook the wemo ground to the box instead of capping it off.
    – Jeff Pritchard
    Jul 11, 2015 at 11:56
  • It sounds like the two black wires are travellers, which means which one is hot will change based on the position of the other 3-way switch. Also, by using the red wire as a "neutral", you'd be connecting the device in series with the lights. This is not good, not to mention you'll need to supply power to the red wire to turn the lights on.
    – Tester101
    Jul 11, 2015 at 13:12
  • Switches are ALWAYS in series with what they control. That's how a switch works.
    – Jeff Pritchard
    Jul 12, 2015 at 11:32
  • that's true for normal toggle switches, but not for smart switches that require power themselves. The switch mechanism is in series, but the power supply is not.
    – Tester101
    Jul 12, 2015 at 11:43
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If the new device requires a "neutral", and there's no "neutral" in the box. You're basically out of luck, unless you can correctly install a "neutral".

Secondly, if the device cannot function as a 3-way. You can't put it into a 3-way circuit, without rewiring the circuit.

It sounds like you may be trying to make dodgy wiring even dodgier. Though I'm not sure what your experience level is with electrical work, so it may be inexperience on your part, not dodgy wiring in the house.

As for why the device powered up. I think the other poster was correct in saying that the red wire on the common terminal, feeds through to the lights. So the device was powered, by being connected in series with the lights (which is not the proper way to do it).

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