2 Way Switch Problem After Changing Switch Plates


Postby Nottmtrucker » Sun Jun 10, 2018 9:11 pm

Hi guys,

Today, I finished redecorating my mother in laws front room and she asked me to swap the light switches over from white plastic to a more decorative one at each end of the room. She had bought the correct switches but after installing them and testing they work, I found that each switch was working as a single switch, where I can switch the light on and off from one switch but not turn it off or on from the other unless the first one is switched off.. I initially thought I may have connected them wrongly but my mother in law said they've always been like that!
I checked the ceiling light and it has red & black power feed, then another red & black cable ( I assume to and from the switch) with the 2 reds connected and one black becoming live and the other neutral.
But at the switches all they have is one cable of brown grey and black. Black to Com, Brown to L1 and Grey to L2.
I thought one switch would have the feed from the light and you would wire the 2nd switch using the 3 colour cable mirroring the connections . Is there a solution without disturbing the plaster? Many thanks in advance if you can understand my problem?
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Postby chriscba » Mon Jun 11, 2018 9:43 am

Could be a junction box under the floor boards somewhere, you'll need some test gear to test continuity from switch to switch.

get a electrician in to test it.
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Postby ericmark » Mon Jun 11, 2018 4:17 pm

In the main two way switching is done switch to switch and has nothing to do with the light.
So at the light there is two core and earth, for clarity I will miss out the earth.

So from light to switch 1 wires from light go to L1 and L2 (not Com) then three core between the two switches like for like, so if grey goes to L1 on one switch it also goes to L1 on other switch.

So to recap with simple on/off pair go to com and L1, with two way pair go L1 and L2.
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Postby Nottmtrucker » Mon Jun 11, 2018 6:44 pm

Thanks for the replies, just recap, I have only 1 cable (3 core & earth) to each switch with L2 (grey) being continually So, am l right in saying I need to find this elusive junction box, hoping it's under the bedroom floorboards?
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Postby Mr White » Mon Jun 11, 2018 7:34 pm

I don't agree with either reply.

First of all you do NOT need an electrician to correct it, you need a competent person. (Or trial and error)

You appear to be saying you only have a 3 core (and earth) since you said

Nottmtrucker wrote:But at the switches all they have is one cable of brown grey and black


If this is true then what ericmark says has to be wrong. Since he says "connect the switch pair then the 3 core" But I have to agree with your first thought of
Nottmtrucker wrote:I thought one switch would have the feed from the light and you would wire the 2nd switch using the 3 colour cable mirroring the connections .


What I would suggest you do (Usual precautions, i.e mains off first) is connect a pair at one switch to com and L1 (Leave the other switch disconnected (But do insulate the ends) Repeat this until you find the combination that turn the light on and off. Make a note of the colours that work.

Now do the same at the other switch (Disconnecting and insulating the wires at the first switch) make a note of the colours that work.

If luck is on your side, you should end up with 1 colour wire that does nothing at either switch.

So you end up with 2 wires that will turn the light on and off (one switch at a time) and one wire that does nothing.

The wire that does nothing you connect to com at each switch.
The two you are left with, one goes into L1 The other goes into L2. at both switches. It does not matter which is L1 Or L2

Switch the mains back on and all should be working.
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Postby Nottmtrucker » Mon Jun 11, 2018 7:58 pm

Well, my friend that sounds promising! I will keep you posted as to the out come, probably at the weekend as I'm away all week. Thank you for your time
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