Trying to replace a light switch in the garage with a new one but the wiring doesn’t match.

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Old switch has white (currently matched to red/black) and black (currently matched to black) coming out of it. Out of the wall there is currently 2 white wires wrapped together but not connected with the current switch. The current switch was also not grounded.

New switch has white, black, red and green. I already tried matching the new switch as white to white, green to ground, black to black and red to black/red and it didn’t work.

2 Answers 2


Well, you're halfway there, and kudos on you for not blindly experimenting as many will tend to. (this can lead to configurations which "work" but will kill you).

I can tell you what is definitely correct:

  • Green to your ground wires.
  • White to your actual neutral wires, and your all-white bundle appears to be both neutral and also neutral for these hot wires. (it matters in boxes with multiple circuits).

So those are done.

Now, you need to double-check the smart-switch documentation to identify the supply-hot for the switch; this is usually black, but that's a convention, not a law. We'll assume it's black; adjust if that's wrong. We are going to cap off the switch's switched hot, and not use it for awhile. Right now the objective is to get the switch itself to power up.

Since you tried black to solo-black, we can cross that one off the list. That leaves the red-black combo, and again, kudos for not breaking up that pair. I would try that pair for supply-hot. Cap off the remaining black wire for now.

If you have two wires on the switched-hot side of the switch, that can only be because you have 2 or more lamps, both fed from the switch. Whereas, if you have two wires on the always-hot side of the switch, that's because you have onward power going to serve other outlets. The second one is much, much more common.

I suspect at this point, the switch will power up. Once you have confirmed some sort of functioning (LED lights, controls work, switch is pairable in its app, etc.), then you can with confidence hook up the switched-hot lead (presumably red) to the remaining unused wire(s).

The only thing that's odd about this - not wrong, but OCD-inducing - is that apparently the cable to the lamp is a /3 cable, with black used as switched-hot and red used as always-hot. Most people prefer it the other way 'round, because then, colors mean something. Code allows it either way.


White in the original switch may have been part of a switch leg not a neutral that your new switch needs, on the new switch I believe you need a neutral if there are several whites in the box tied together that is usually the neutral but a single white may actually be a hot, the hot normally a black in the box but could be a white if s switch leg goes to the black and the red on the switch is the switched hot normally going out on a black wire. I cannot see the wires in the back of the box but this is how I would wire it if it did not work I would check to verify the black hot to white has 120v.

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