So, 40 yr old townhouse, there are two ceiling lights in the "rec room" area of the bottom floor/basement. Two dimmer dials/switches (push in for on or off, twist for dimmer function) in one receptacle near the doorway. One died, so i decided to update with some nice LED-rated Lutron dimmers (toggle + slider).

Pull off the faceplate, pull out the dimmer units, and the dimmers both have two black wires coming out, no identifying marks. Out of the wall, there's a black, a red and a white wire. I was not smart, and did not take a picture, or keep track of which wire went where, relying on the Lutron instructions to get me though it. Turned off the breaker, and removed the old switches, and wired the new switches in what I thought was the right way according to the instructions.

Well, one switch now turns on both lights, and that slider dims both lights, the second switch does nothing, but the slider dims one light.

The Lutrons have Black, Red, Red-White and green(ground, which i will eventually screw to the back of the junction box).

I've gotten as far as the black is common hot, so the red and the white must be "traveller" wires to the separate light fixtures, and i tried wiring the red on each dimmer unit to those, one to red, one to white. Different, but similar behaviour on the switches and sliders.

Any advice (other than "call an electrician, ya mook!")?

  • 1
    Traveler wires don't come into play unless the light is controlled from two switches. The number of lights has nothing to do with it, any number of lights equals 1 light as far as the switch(es) are concerned. Commented Sep 21, 2018 at 19:26
  • 1
    Are there any other wires inside this junction box? Nutted together or pushed into the back? Commented Sep 21, 2018 at 19:28
  • Probably one of the wires is the line hot (always hot) and this is to be connected to the line hot of both switches. The other two are switched hots--one goes to the switched hot contact of one switch and one to the switched hot contact of the other switch. Identify which wire is the line hot. Commented Sep 21, 2018 at 21:01
  • there's probably no neutral in that switch box. you won't be able to use dimmers that require three wires.
    – Jasen
    Commented Sep 22, 2018 at 5:15
  • Are these Lutron dimmer switches capable of 1-pole or 3-way use? If used as 1-pole switch, is one of the wires either not used or connected to one of the other wires? Commented Sep 24, 2018 at 15:23

1 Answer 1


I think you have mis-identified the "hot" wire. Do you have a multimeter? Assuming your box is actually grounded, carefully measure the voltage between the red, black and white wires to the box. If only one has 120 volts on it, then that is your hot wire. If 2 wires have 120 volts, then someone did a bad thing and wired the switches to break the neutral.

Another way to identify which wire is hot is to pull down the light fixtures and examine the wiring. Don't disconnect anything without taking notes about how it was hooked up first!

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