Ran into an issue trying to replace a light switch with a Lutron dimmer switch. There are three switches for the light. As you can see from the photo, I have 5 wires into the current switch. I only have 4 wires on the Lutron (Red, Black, Red, Green).

Any help on matching up the wires with the switch. enter image description here

  • The different switches control the same (set of) lights? In the US, that's called a 4-way switch setup, and you'll need to make sure your dimmer switch is set up for a 4-way. IIUC, you need two 4-way switches and one 3-way for your configuration. It would help if you posted the model number of the switch you already have - it could be that you can replace the 3-way switch instead of this one.
    – FreeMan
    Jan 15, 2022 at 21:51
  • Additionally, it is strongly recommended to not use those backstabs (where the wire is pushed into the hole in the back of the switch/outlet). They can work loose over time and cause breaker trips, or worse, fires.
    – FreeMan
    Jan 15, 2022 at 21:52
  • Yes, the different switches control the same set of lights. Here is the dimmer that I want to use. link So I'll need a different dimmer switch? Jan 15, 2022 at 22:29
  • 1
    Yes, the drawing in diagram 4B indicates that this switch is 3-way capable (most actually are these days). Go find one of the other switches that has only 3 wires (plus ground) and replace that one.
    – FreeMan
    Jan 15, 2022 at 22:49

1 Answer 1


What you're looking at there is a 3-way switch. It's not a 4-way even though it has 4 wires.

enter image description here

Black screw is common, brass screws are travelers.

What's happening there is that the switch has both side screws and backstabs. Each backstab is electrically connected (continuous) with the nearest side screw. And so, the installer is using this feature to also splice the two black wires to each other.

This very strongly suggests the 2 black wires are "supply always-hot" - one from supply and the other taking it onward to other switches or points of use elsewhere. It might be something else, but that's probably irrelevant to the switch wiring.

Yes, I know there's a third black, but I'm a huge fan of using colored electrical tape to identify wires by function - like this.

enter image description here

Now you know what the wires are doing, you'll need to connect the Lutron dimmer according to its instructions. It goes without saying that you need a dimmer capable of working in a 3-way circuit, but from the wire colors you describe, this is likely the case.

  • Thanks everyone. I was able to swap out one of the other switches as suggested here. Everything works great! Jan 25, 2022 at 21:41

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