I have 3 switches controlling ceiling cans. I wish to replace one switch with a 3 way dimmer. The box has 4 wires. 2 black. 2 red. One black completes a circuit with one of the red wires. The other black completes a circuit with the other red wire.

How do I connect a dimmer with one black and 2 red wires?


  • Oops. Thought you said fans. You said cans. That should be easier! Please upload pictures showing the existing switches/wires. Commented Nov 12, 2020 at 15:26
  • Can you post photos of the insides of all switch boxes involved? Are these ceiling cans over a staircase, perchance? Commented Nov 12, 2020 at 23:24

1 Answer 1


(I am by no means any sort of expert, but I hope this points you in the right direction at least. I'm not an electrician but randomly looked up stuff about switches before because I was curious why they were called "3-way".)

You mentioned that there are three switches controlling the lights. That means there are two 3-way switches and one 4-way switch. The Wikipedia article on this does a much better job explaining than I can. Essentially you need 3-way switches to have two switches control one light, but you need 4-way switches to allow for more than two.

You said the switch you replaced has 4 wires. Sounds to me like you're looking at the 4-way switch from the middle of the circuit. I would guess you bought three 3-way dimmers and replaced the other two without issue but are confused with this one. I think you simply need a 4-way dimmer.

Using three switches

  • 1
    Thing is, 4-way dimmers are quite a non-trivial thing to do (it's possible by abusing a special type of dimmer + some relaying, but it's a hack all the same, and not up to current Code in situations where multiway switching is a Code req, not just a convenience function) Commented Nov 12, 2020 at 23:23

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