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I’m swapping out a single light switch for a smart switch. The wiring from the gang is a single cable with red, black, ground, white. The neutral wire was unused in the original switch. The smart switch has the same wiring configuration and the instructions say to match colors. On the others I have installed (same switch same mfg) everything works fine but when I match the colors and connect it all I get nothing. I’m wondering if the neutral wire is not connected somewhere down the line like in the light itself. All other components work fine and the single pole switch works when reinstalled enter image description here

  • What is the model # of the new switch? Which wire from the wall is hot, black or red? One of them (and only one) should show ~ 120V to ground and to white (presumed neutral). You should have no voltage between white & ground, and the same (~120V) between whatever is hot and both neutral & ground. – manassehkatz Jan 16 at 21:16
  • Can you post a photo of the box for the light? – ThreePhaseEel Jan 17 at 0:14
  • Your sure that was a single pole switch and not a three way switch? If not three way sounds like you have no neutral. and need to trace down wires. – user101687 Jun 15 at 18:49
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Red and black are not always going to match up like that. I'm pretty surprised the instructions even mention matching colors. There are conventions, but it's not very reliable in practice other than white always being neutral and green/bare being ground.

You need to read the instructions on your smart switch, and you will find that red or black is going to be for power (line) and the other is going to be for the light (load). Since it's not working the way you have it hooked up, I would assume red and black need to be swapped, but before you ruin the switch, read the instructions and determine if the red or black wire in the wall are hot (line voltage).

More explanation: On a regular switch, what wires are hooked up to the two screws doesn't matter because it's a simple contact closing and the electricity will flow either way. On the smart switch, it needs power on a particular wire to control the electronics. So, the hot wire from the wall must be connected to that particular wire on the switch and the load (light) gets hooked to the other wire.

  • Thanks for the response. I’ve tried that...I think I’ve tried every combination of colors. I wired the switches the way the instructions and 127 different YouTube guides have said and the 2 in the other bedrooms work perfectly. This room is the odd duck. – Ben Jan 16 at 21:08
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    Have you tested the voltage between the wires with the power on? There should be 120v between red and white or black and white. If not, look inside the box for the light - the white wire might not be connected to anything. Whats the model of the switch? – JPhi1618 Jan 16 at 21:14
  • White isn't always neutral. Neutral is always white (or grey ). – Harper Jun 15 at 17:34
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It looks like you have mixed up the wires. You haven't mentioned which wires were initially connected to your switch. And a clear photo of the smart switch is needed to see which wires should be connected there. You almost never need an earth wire to be hooked up to a smart switch. Just remove that one. You only need to connect 3 wires to your smart switch in this configuration. Live and neutral as the input and just one output wire.

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