I had a workman come round this morning and he had to detatch the light switches. Afterwards, he put them back on again, but something seems to have changed and I know that I need to swap two wires around but not sure which...!

In the hallway, I have one light that is controlled by two light switches. Currently, the switches are wired as follows:

Switch one: Top left brown, Top right blue, Bottom black.
Switch two: Top left brown, Top right white, Bottom brown. (It is an old flat, so I'm not sure that the colours on this switch are per the norm)

However, in this constellation, although switch one works properly, switch two acts as a master, i.e. switch one only works if switch two is on:

Switch two = on... Switch one can be used to turn the light on or off.
Switch two = off... The light is off regardless of what position switch one is in.

I assume I just need to switch around the two top wires in switch one, but I wanted to check it with people in the know first...!

Switch 1 Switch 2

  • It wont be the 2 wires in the top of the switch that need swapping, it will be one of the top ones and the bottom one that has been swapped.
    – HandyHowie
    Feb 15, 2023 at 12:57
  • 1
    Why not call the workman back to have him fix what he broke? I know that's not the DIY answer, and this is an opportunity for you to learn, but hold him accountable or he will never learn!
    – FreeMan
    Feb 15, 2023 at 12:58
  • Is it the one with the black wire or the one with the white wire that is acting as a master?
    – HandyHowie
    Feb 15, 2023 at 12:58
  • Classic symptom of a three-way switch wired "backward". One of the two poles got swapped with the common, effectively turning it into a simple switch. Your handyman is less careful or less competent than s/he should be.
    – keshlam
    Feb 15, 2023 at 15:50
  • Whatever you do, don't call an electrician to come fix it. Feb 15, 2023 at 18:55

1 Answer 1


It's weird that there are no matching wires on both sides. This indicated that somewhere those wires get spliced. You might be able to find that junction point (possible a third switch) and make sure that wasn't messed up as well.

Because we can't use colors we'll need to do some testing. If you have a way to check continuity then we can do a fairly simple test.

First turn off the breaker to that light, then check that the power is off at that location.

After you have made the circuit safe, at one switch connect all wires together. Then you can check continuity between the wires at the other switch (disconnected from the switch). The ones with continuity between them will be the travelers, those should be the ones going into the top contacts. Do the same test the other way around.

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