I have a smart light switch with a connecting wire for ground, neutral, light and switch (a green, white, and 2 black wires). It was previously connected to a smart switch and I'm just changing to a different smart switch.

There are 3 cables coming from the wall. Each cable has a bare copper wire, a white wire, and a gray wire. The 3 coppers are wound together and I understand these to be the ground. The 3 white wires are also wound together and I understand these to be the neutral wires. But I don't know what to do with the remaining 3 gray wires.

I have tried putting two of the grays together and attach to one of the black wires from the switch and put the single remaining gray to the other black wire. One of the possible configurations of gray wires resulted in the light being on but the switch not working, and the other configurations resulted in nothing at all working.

I don't believe this was a 3-way switch since it's a small room with just the one switch. Otherwise just outlets and an Ethernet cable port. I also live in the US and I know this room was finished by the previous home owner who did it himself. light switch markings light switch wiring

  • 2
    do you remember how it was connected originally? Commented Nov 29, 2023 at 14:14
  • No, I failed to take a picture or anything since all the others I did were simple with red and black wires that I could put together Commented Nov 29, 2023 at 14:16

1 Answer 1


The most likely option is that one black (gray) is from the breaker, one goes to the light as a switched live, and one goes to another switch to power the lights there as a unswitched live.

If all blacks are disconnected you will find that another light or outlet is not working. If you find that you can figure out which of the wires goes where by connecting 2 of the three together, restoring power and seeing what happens.

Failing that you have a multimeter you can find which one is the feed by checking each black against the neutral bundle when the power is on.

I can't quite make out the marking on the switch but it's likely that the feed and the switch live have specific places and cannot be swapped.

  • I will try that. Say I figure out which wire goes to an outlet or other switch, how do i shirts which wires go where on the switch? (I added a better picture of the light switch markings) Commented Nov 29, 2023 at 14:49
  • 1
    The lightning bolt goes to the feed, the incandescent bulb goes to the light. Commented Nov 29, 2023 at 14:55
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    You connect the incoming hot to the outgoing unswitched hot and the switches hot, @BrockLarson. Then you connect the switch's outgoing switched hot to the black that goes to the fixture you're controlling.
    – FreeMan
    Commented Nov 29, 2023 at 17:14

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