I have wired a new 3-way circuit in a bunk-house exactly as shown in the following diagram, with wire types and colors matching those in the diagram 100%:

3-way wiring diagram

I have a 2-pack of Leviton 6674 Dimmers, which came with the following wiring instructions:


It is confusing me for the following reasons:

  • The instructions are written as though someone is replacing existing switches (referencing the screw-colors on the old switch) but since my circuit is new, I don't have that to reference.
  • The example circuit in the instructions doesn't match the one I've wired in the diagram above.
  • The wires coming out of the back are not colors that match the colors of the wiring. The switch has: - two red wires (one is tagged with red tape also), one black wire, and a green ground wire as follows:
    enter image description here

Can anyone tell me in simple terms (keeping in mind I don't fully understand terms like "common", "line/load", etc), and specifically based on the exact wiring diagram above, how exactly I should connect the Leviton switches (i.e. which specific wires on the back of the switches should connect to the specific color wires in the boxes?

EDIT - I somehow overlooked the note in the instructions that you can only use one dimmer in a 3-way application. Let's say I'll put it in the 1st box (the one on the left of the diagram) - I'm still confused on which switch wires to connect to each of the three colors in the box...

5 Answers 5


It's confusing to you merely because you are a novice in this area. This is normal and all will be explained as you learn. A few things:

  • In mains electrical, color codes often mean far less than you'd hope. Cables are made that way, with the same 2-3 wire colors, and gets used for everything. The colors are to distinguish the wires from each other, not define meaning/purpose.
  • In 3-way circuits, colors are worse than useless because you have 4 functions and 3 colors to define them, and no two circuits are alike. Even experts have to work through it, it's ridiculous. This is why I intentionally use colored tape to remark the wire color by function. It turns insanity into easy mode.
  • You are learning "by rote" - that means repeating a thing mechanically without functional understanding. That falls apart in a hurry in 3-way circuits since every one is different.
  • Instructions cannot possibly tell you how to wire when every circuit is different.

Code requires that neutral be white (if it's present). I prefer color codes of black for always-hot, red for switched-hot (hot when you want the light on), and yellow for travelers. Now, a 3-way looks like this

enter image description here

and wires like this

enter image description here

So get a 5-pack of colored electrical tape. On your spur cable to the lamp, mark the black wire red on both ends. On the /3 cable between switches, you are using red and white as travelers, so mark them yellow. Now you're marked just like this diagram.

What about that dimmer? I'll sneak you to the end, although given what I just showed you, it may be fairly obvious. The two red wires are travelers. Mark them yellow. And voilà, everything should make sense.

But this may violate Code

Ugh. All this and we have a problem. Depending on the application, it may violate the building codes. You notice that most of the time, switches are in an obvious place: that's because Code requires that. Certain (most) switches are required, and required switches must turn on a light and give usable light. This is to benefit guests (so they don't hurt themselves) and first responders (so they can work).

The wiring of this dimmer forces you to put it in one location (only place you have black-yellow-yellow, the far switch). If the dimmer is turned way down, flipping the switch at the other location would provide a very dim light. That's a Code violation since the switch doesn't turn on a light in the room.

The way to fix that is smart dimmers where you have a dimming control at each location.

Some smart switches use wireless or power-line signaling. Your wiring layout lends itself well to smart dimmers with a wired communications line. In that case, the between-switches /3 becomes black=always-hot, white=neutral and red=communication. This also gives you always-hot and neutral at the far switch if you want to extend the circuit.

  • Thanks for the fantastic and clear explanation. I'll be back at my cottage in a few hours and I will give it a go. Also, RE: the potential code violation - would this be mitigated if the one dimmer switch is located at/near the entrance?
    – GWR
    Commented Aug 1, 2019 at 15:44
  • You are good Harper.
    – JACK
    Commented Aug 1, 2019 at 21:56

There is no possible way to wire two 3-way dimmers into the same circuit. Doing so will reduce the ohms (resistance) in the circuit and cause a short, and neither of the dimmers will be able to operate the light(s). If you want to install the dimmer, it has to be one three way switch and one dimmer switch.

The .pdf instructions you provided shows this clearly in Step 5b. Also, under 'Warnings and Cautions' at the top-right side of the instructions, it states: "Use only one (1) dimmer in a 3- or 4-way circuit. The switch(es) will turn the light on at the brightness level selected at the dimmer". In other words, all of the lights on the circuit will be at the same brightness level as the setting on the dimmer.

The Leviton website also describes the 6674 dimmer on their website by stating "Single pole or 3-way lighting control when used with a 3-way switch".

  • I somehow overlooked that warning in the instructions, but it makes sense. So let's say that I use 1 dimmer at the 1st box (the one on the left of the diagram) - I'm still confused on which switch wires to connect to each of the three colors in the box...
    – GWR
    Commented Aug 1, 2019 at 11:15
  • The wiring depends on what component the line coming into the circuit is connected to first. If the "hot" wires (the wires coming from the electrical source) connect to a light fixture first, the circuit is connected one way. If the hot wires connect to the switch or the dimmer first,the connections are different.
    – chuckiii3
    Commented Aug 1, 2019 at 11:29
  • It's 100% identically wired as in the first image in my main post.
    – GWR
    Commented Aug 1, 2019 at 11:30

Sorry for being so confusing earlier this morning - I was tired and not completely "with it" yet!

Wiring this is rather easy. One simple rule to remember is that switches (and dimmers in your case as well) are always wired "hot". In other words, only Black or Red wires are ever connected to the switch (or dimmer) itself. In your particular installation, however, a White wire is in fact used as a "hot" wire on both the dimmer and the switch. In this case, the White wire must be colored Black or otherwise identified as a "hot" wire by wrapping it with a piece of black electrical tape. This is how to wire your circuit:

Identify the Black and Red wires coming out of the SAME SLOT on the back of the dimmer. Using your original image - not the one posted by 'Harper' - the Black wire on the dimmer is connected to the Black wire going to the light fixture(s). The Red wire on the dimmer is connected to the Red wire going out to the switch. The other Red wire on the dimmer (the one in the same slot as the Green ground wire) is connected to the WHITE wire going to the switch. Mark the White wire as being Black because it is now "hot". The Green ground wires are all connected together in the box.

Wiring the switch is equally easy. The Black wire connects to the brass screw on the switch. The Red wire connects to the silver screw on the same side of the switch as the Black wire. The White wire, which must also be identified as Black with a piece of electrical tape, is connected to the other silver (or common) screw on the other side of the switch. Finally the bare Ground wire is connected to the green screw on the switch. Wiring the light fixture(s) should be self-explanatory. And that's it.

Finally, in my humble opinion, I think Harper's explanation and diagram, while slightly different yet certainly correct, is a bit confusing - the reason being that coloring some of the wires Yellow seems to be an unnecessary step (other than to help you visualize the circuit diagram more easily). It's very obvious that Harper knows his stuff, but I think it's easier to wire the circuit using the typical Black, Red and White color combinations without introducing yet another factor into the equation.

In any case, I hope we've been able to help you! Let us know when you get everything working!!!


You CAN have two 3-way dimmers on the same circuit if you use smart switch such as Lutron’s Caseta. This is possible because one dimmer is wired and the other is operated by Bluetooth. Works very well. You can even controll the dimmer through Alexa or your smart phone. Im not, by any means, an electrician and I was able to set up my kitchen and hallways.


As others have alluded to, using standard electronic dimmers in a 3-way application is not possible in the dimming function. You can however have a dimmer wired in 3-way application to a 3-way switch so that you can turn on and off the lights in both locations, but you can only dim the lights at the one location.

There are solutions that are available from Lutron, Leviton, and a few others that will allow for the 3-way dimmer control but those are typically more expensive and utilize wireless technologies to have a master dimmer at one location with a remote control at another.

The conversion of the wiring using these systems could get a little complicated so a licensed electrician would be recommended to investigate the existing wiring and wire up the new controls properly. I would imagine the cost is relatively minimal for this service.

  • Note that the Leviton and Lutron systems apparently use power-line communications over the traveler wire, not wireless of any description. Commented Jan 12, 2021 at 12:37

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