How do I upgrade a 3-way light switch with dissimilar wiring?

I’m upgrading two light switches in my kitchen. I’m replacing the existing 3-way switches installed God-only-knows how many years ago with new 3-way dimmers capable of handling LED and CFL bulbs.

I’ve always understood home electrical wiring colors to be: white/gray is neutral, green (or just bare) is ground, black / red / blue is usually hot.

When I took off the cover plate to the existing switch what I found was that it had the expected neutral and the two load wires – black and red. There was no ground wire on the switch, which was strange.

However the new switch has the ground wire as expected, but no white wire and instead has two red wires and a black wire. 4 wires total, no obvious neutral. The red wire closest to the ground wire has a label on it that says to the effect “only use when wiring in a 3-way circuit.” Okay. That doesn’t help. That must be one of the load wires but where’s the neutral? I expected to find a white wire, two black or red wires, and the green ground. That’s not what I’m seeing.

So how do I install this thing? I’m hesitant to just start twisting wires together hoping for the best.

Was a bit confused on your description, so perhaps a diagram would help.

That’s what I’d expect. Lots of older switches weren’t grounded. Both the black and red are hot.

I am also confused by the new switch. I agree you should have a clear neutral. I’d read the instructions very carefully. Are the wires directly attached to the switch, or do they have terminals that existing wires attach to?

Here are the installation instructions for the new switch – same make and model. Note in the 3-way instructions it has the wires marked as 2 red, a black, and the green ground. That’s what I see on the switch.

I’ve taken pictures but apparently can’t upload them to my posts.

The wires are directly attached to the switch, no terminals at all.

The ground is the ground obviously. Your new switch just switches the hot. The hot comes into the switch on black, and hot goes out to one or other of the “travellers” to the other three way, then to the light, and from the light to neutral.

The neutral does not pass through the switches

Be careful - that “neutral” may not be neutral if it goes to the switch. Again, see @Crafter_Man’s diagrams. You have a hot wire going into the first 3 way switch and a “hot” wire going out of the second 3 way switch, and two “switched hots” in between the two switches. If the switches are set the same way then the light turns on. If the switches are set to opposite sides then the light stays off.

On older wiring it is possible that they used the neutral as the “ground”. It is also possible that they used the “neutral” as one of the hot connections, in which case they were supposed to put black tape around the end of the wire to indicate that it is actually a hot and not a neutral. I have seen many cases where no one bothered with the tape.

Make sure you figure out exactly what you have before you start disconnecting and reconnecting things.

Depending on the age of your wiring, it’s not strange at all. If it’s 1960s or earlier it most likely wouldn’t have a ground.

Well, the “neutral” may very well only be at the light. Not at any switch location. Looking at your diagram your switch does not require a neutral. That’s good. Grounds are a separate subject, may not be present, and can generally be ignored from a functional standpoint ( Safety. Ground everything always. Everytime.)

If you have a three way switch, and three wires to that switch, then the white is probably not what you expect it is.

There is, at each three way switch location, three wires that matter for lighting control. One hot and two travelers at one, then two travelers and a load wire at the other. As crafter mans diagram indicates. The load wire extends to the light(s) where the neutral joins, likely from a different cable assembly.

The white should actually be a constant hot in this situation but that is an often disregarded rule.

Edit: I made a post on the how to of discovering which which wire were which on a three way awhile back. I’ll look it up if you’re feeling adventurous.

Perhaps that was my issue: I’m so used to white being neutral that I assumed my white wire was neutral but of course in a standard single pole switch it simply interrupts the hot side while the neutral is bypassed.


Built in 1967, some minor updating in 1984. Nothing since then.

I have a multimeter but haven’t a clue how to use to help me here.

One general rule, which is probably true the world over, is: “Never make any assumptions about wires based on colour.”

"When I took off the cover plate to the existing switch what I found was that it had the expected neutral and the two load wires – black and red. There was no ground wire on the switch, which was strange."

If you had 3 wires connected to the switch then 2 were travelers and 1 was either load or the hot. If you do not know how to use your multi meter to determine which are which it is best for you to get someone in to help you.

Bob_2 you are so right. I just worked on a light fixture. The white wire to the fixture is the hot lead and the black wire is the switched neutral. Some where in this house a earlier owner crossed wires in an outlet box.