2 way 2 gang switch. Help please.


15 May 2011
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United Kingdom
My hall and landing both have 2 gang 2 way switches controlling the lights at the top and the bottom of the stairs. This worked fine, but I replaced the switches when decorating and now can't get the lights working correctly. I have searched similar posts on this forum, but can't find the same issue.

The downstairs switch has 2 x 3 core cable (red, blue, yellow)
The upstairs switch has 2 x 3 core cable (red, blue, yellow) and 1 x 2 core cable (red, black)

My understanding is that the 3 core cable should simply connect each 2 way switch and the 2 core cable goes to the light / live, so I'm not sure how the downstairs light works at all without a 2 core cable from the switch to the downstairs light.

I currently have it wired as follows:
Upstairs gang 1:
COM = red (from the opposite 3 core cable than the blue / yellow)
L1 = blue + red (from 2 core)
L2 = yellow + black (from 2 core)

Upstairs gang 2:
COM = red (from the opposite 3 core cable than the blue / yellow)
L1 = blue
L2 = yellow

Downstairs gang 1:
COM = red
L1 = blue
L2 = yellow

Downstairs gang 2:
COM = red
L1 = blue
L2 = yellow

Connecting the red wire from the 3 core cable to the COM connector in the opposite gang seems wrong, but it was like this originally and is the only way I can get anything at all useable.

When the first upstairs light switch is on, the second upstairs switch correctly controls the downstairs light, the first downstairs switch correctly controls the downstairs light and the second downstairs light correctly controls the upsatirs light.

When the first upstairs light switch is off, the second upstairs switch and the first downstairs switch no longer work and the second downstairs switch now controls the downstairs light.

Hopefully this all makes sense - I can post some pictures, but not sure that it will make things any clearer. Any help in understanding this is greatly appreciated.
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You don't need a 2 core and earth (red and black) switch wire if a joint is done at a junction box or at the ceiling rose.

Your message implies the red commons of the 3 core and earth cables have been mixed up.

Please firstly be aware which terminals are for which switch - some posters on this forum cannot tell that certain terminals are for one particular switch. This could be why the reds are mixed up.


L1 L2

is a typical arrangement for most switches.

It seems you shouldn't have 'opposite' reds to the blue and yellow as you have desscribed.

Before explaining how to put this right, are you able to test where each cable goes to?

And don't forget, you may have to isolate more than one fuse/circuit breaker to isolate the power.
Thanks for the quick reply sparkwright.

I can't test the cables - I'd already decided I need to get a multimeter, but don't have one yet. I'll be getting one in the week.

The terminal for each switch are as you describe:

L1 L2 / C
C / L1 L2

The old switches were slightly different, hence the mistake in the re-wiring.
Let's call the cables;
CABLE A two core (red and black) switch wire from landing light
CABLE B 3 core from landing switch top to landing switch bottom
CABLE C 3 core for hall switch top
CABLE D 3 core for landing swich bottom

So, upstairs switch position will consist of A, B and C
downstairs switch will consist of B and D

Upstairs switch gang 1
Com = red of B
L1 = red of A, blue of B
L2 = black of A, yellow of B

Upstairs switch gang 2
Com = red of C
L1 = blue of C
L2 = yellow of C

Downstairs gang 1
Com = red of B
L1 = blue of B
L2 = yellow of B

Downstairs gang 2
Com = red of D
L1 = blue of D
L2 = yellow of D

Be sure to earth the faceplates if they are METAL.

Make sure to turn off both up and down lighting circuits.

Make a note of which cable is which so you don't get in a muddle.
  • Thanks
Reactions: rbt
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Got it sorted now. Many Thanks sparkright.

The red commons were wired the wrong way round in the downstairs switch. I'd fooled myself into thinking the problem was upstairs so was focussed on that.

Cheers mate!

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