Cannot find the common wire in “box #2” on a three way circuit

Question

I have a three wire circuit wired incorrectly and it doesn't work the way it should.

If the switch with the hot wire is switched on (Box #1), the other switch works as it should (Box #2). However, if the switch in Box #1 is switched off, the Box #2 switch doesn't function at all.

I have a multimeter and was able to locate the hot wire in the first box, and found continuity on the two traveler wires in box #2. The problem is, the remaining wire is not black, it's red and there is ZERO continuity between the hot wire and this remaining red wire.

In this same box (box #2) is a single pole switch that controls the fan motor. I tried taking the not-hot black lead and switching it with the red lead that should be the common for the fan light, but then nothing worked. Not the fan, not the light. I am stumped at this point.

The switch with the hot wire almost works like a drop leg circuit instead of the way it should. Should I take ALL the wires out of box #2 and test each one until I find one that has continuity with the hot wire from box #1?

Answer 1

One way to wire a 3-way switch:

             ---                  ---
            | ^ |---Traveler 1---| ^ |
---Line-----| | |                | | |-----Light
            | v |---Traveler 2---| v |
             ---                  ---
             SW1                  SW2

In the above diagram, power comes into Box #1 and the switched hot for the light exits in Box #2. From your description, I think this is what you have, but wiring will change depending on the location of the "power to light" wire (load).

When SW1 is in the up position, it connects the hot line wire to Traveler 1 (T1) (Up could be traveller 2, but the concept is the same). When SW2 is in the up position, it connects Traveler 1 to the load. If SW1 is then flipped down, power travels on traveler 2 (T2), and the light is off because SW2 still has T1 connected to the load. If SW2 is flipped down, T2 is connected to the load and the light turns on.

As you can see, SW1 diverts power to T1 or T2 depending on its position, so you can identify the two travelers as the wires that are alternately hot when SW1 is flipped. The travelers should be connected to the bright (metal colored) screws. Line and load are connected to the dark colored screws. Once you have correctly identified Line, Load, T1, and T2, make sure they get connected to the correct screws.

Box #2 will have the two travelers, a load wire for the light, load wire for the fan, and probably a line wire for the fan (the other switch in that box should have the line and load for the fan). Of course there will be neutrals and grounds in both boxes, but those shouldn't come into play. It's possible a white wire is being used as a hot in a "switch loop" if you find one connected to a switch. If you find that, put some black tape on it to mark it as a switch loop hot.

Answer 2

You may be confused as to how 3-way circuits work, since you seem to be expecting certain colors, and are discussing "on" and "off". 3-ways do not have "on" or "off", they merely have "traveler 1" or "traveler 2".

The two travelers are interchangeable, and always run together in the same cable (with a third wire to complete the circuit). They are almost never yellow, but I recommend you mark them with yellow tape on both ends - it makes it a lot easier to understand and work in 3-way boxes.

They can be any combination of the wire colors in cable - red/white, black/red, or black/white. This can even change in the same circuit! That's why I recommend re-marking them.

I am fond of picking the traveler colors so that the remaining wire is the color of its function: white if neutral (in fact this is mandatory), black if always-hot, and red if switched-hot.

Once you are clear which wires are the travelers, make sure the travelers are landing on the brass screws on the 3-way switch. The black screw goes to the always-hot or switched-hot.