I'm trying to fix an uncompleted installation of a two-way switch.

One switch, the light and all the wiring have been installed by someone else, with whom we can't have any contact soon.

I bought the second switch and tried to install it. I blindly tried different combinations and had those results:

  1. With some wire combinations, it didn't work at all.
  2. With some others, it worked 3/4 times, but in some positions, one switch didn't work until I reached the other one.
  3. When bridging all wires of the second switch together, the first switch controlled the lamp (ON/OFF) -- but I now doubt it, maybe some of them wasn't wired correctly?

In no case was it working fully as expected, but I didn't try all combinations.

I have a basic understanding of the way it should work when everything is wired correctly.

I tried to systematically understand the consequences of inverting wires in all combinations, and came to the conclusion that it should either

  1. work as expected
  2. work 3/4 times
  3. everything is shortcut and the light is always on

So, if I understand correctly, the wiring is wrong. The colors seem random and non-standard, so I can't rely on that.

Is this correct? Is this something I can easily fix?

UPDATE: each switch is connected to 3 wires coming out of the wall.

UPDATE 2: I'm living in Belgium, but the colors of the wires in my walls don't seem to be the national, or even less the European ones ;-)

  • Colors can depend on where you live, en.wikipedia.org/wiki/Electrical_wiring#Colour_code Dec 6, 2014 at 15:45
  • Outside of the color problem, this is the same as diy.stackexchange.com/questions/52664/…. The discussion there may help you understand why getting a switch "backward" will have this effect, and the suggested how-to-fix-it sequence at the end of that post doesn't actually require identifying the wires if the colors are semi-rational.
    – keshlam
    Dec 6, 2014 at 17:40
  • (... Assuming the switches and wiring work. See my comment on @ratchetfreak's answer, where you provided some additional information about what happens when you bypass a switch.)
    – keshlam
    Dec 6, 2014 at 17:47

1 Answer 1


Look at the other switch; there should be 1 coming in; a black live, and 2 travelers black and red or black and labeled black coming out. The neutral will just be pigtailed. If there is just a single switched live going out then you will need to run an extra wire to the other switch.

To make a single switch into 2 you need an extra traveler (switched live) between the switches.

enter image description here

  • What do you mean by "the other switch"? Each one has 3 wire. The colors aren't consistent with what you say or anything that I could find on the net. I think they are almost random.
    – ymajoros
    Dec 6, 2014 at 15:40
  • @ymajoros the one already there. Dec 6, 2014 at 15:42
  • I remember 2 blue wires and another one.
    – ymajoros
    Dec 6, 2014 at 15:43
  • @ymajoros where do you live each country tends to have it's own convention red and blue is common in Europe. Dec 6, 2014 at 15:44
  • I live in Belgium, but those colors seem to be the random invention of the person who installed it. I looked it up and it seems I shouldn't see those colors, so I'm trying to understand my problem without counting on them ;-)
    – ymajoros
    Dec 6, 2014 at 15:47

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