I am replacing a light switch that contains two modules ie two gang two way and each module is labelled “Common, L1 & L2” and works perfectly this way and with the other switch. All have one or two wires in each connector.

However the replacement is a single module labelled “L11, L1, L12, L21, L2 & L22”. I am completely fixed and tried numerous combinations.

So my question is on the new module if I take the old module as a and second as b and new as c where does a-common go in c etc


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  • 1
    You need to look at the wiring diagram that came with the switch. It might be on the inside of the box it came in. Post a picture of it. – JACK Sep 11 at 14:10
  • Purchased of the web and no instructions. Contacted supplier and they gave me a diagram with incorrect references, but thanks anyway :-) – GordyB Sep 11 at 17:29
  • Use a multimeter to verify the pairs that get make/break as each switch is flipped. Those pairs will be the equivalent of the L1, L2 on the originals; the remaining 2 will be the "common" aka "return" . The answers state this, but I like to test anyway when a switch comes with ambiguous documentation. – Carl Witthoft Sep 11 at 17:59
  • Did the package come either from outside the EU or from an Amazon warehouse? Return it. Those are not safe nor legal for use in your country (or any country, probably not even China). They are cheating EU law, which requires the importer be responsible for safety certification. When it ships from China/Amazon, you're the importer. – Harper Sep 11 at 19:26
  • The CCCs mark, whose origin is itself dubious, could also be faked with impunity, it's only applicable to products sold inside China. There are no treaties that make CCC meaningful in the EU the way UL/CSA/ETL are. – Harper Sep 11 at 19:35

I can only see L1 and L2 labels, so L1 will be Switch A and L2 will be Switch B. The terminal at one end is the common, and the two at the other end are the changeover/travellers.

It should be basically the same layout, but rotate one of your existing switches through 180 degrees. I.e. your existing switch has both commons at the top, but the new switch has a common at the top and a common at the bottom.

2-way switch

These are coloured lines only, not wiring colours.


L1 is common. L11 and L12 are equivalent to L1 and L2 on the original switch.

L2 is common. L21 and L22 are equivalent to L1 and L2 on the original switch.

  • Brill thank you so much I will have ago on Friday :-) – GordyB Sep 11 at 17:31

A single 2-way is hard enough. A double 2-way is confusion waiting to happen!

The old L1 and L2 on each switch are what we call "travelers". They are a matched pair, and one is hot or the other one is. They are interchangeable. As such, I like to mark them both yellow with tape. I prefer to wrap the tape around the wire as far back as practicable.

Now here, you have two complete sets of travelers, and you must match each pair to their partner common wire. In some cases, this is completely obvious, e.g. Both travelers and common are in the same cable. Other times, it doesn't matter because both commons are split from the same wire. **But if it's any other thing, mark the commons also in some way to associate each with its travelers.

For instance you might mark one set of travelers blue and the other yellow, and then mark their common with a half-width piece of tape of the same color.

While the old switch is still on, marking will seem like a useless chore. Why not just move the wires over, one wire at a time, and not make any mistakes, and not get confused at all? Heh... You know what happens there. It's practically inevitable. And honestly, most likely we would not be able to help you much at that point. It would take some fairly complex probing.

Anyway, on the old switch, you can tell how it's split - C is common, L1 and L2 are the travelers.

On the new switch, Lx is common, and Lx1 and Lx2 are the travelers. X is 1 or 2, of course.

  • Brill thank you so much I will have ago on Friday :-) – GordyB Sep 11 at 17:32
  • @Harper Purchased over internet.... Provided incorrect info ... problems??? – JACK Sep 11 at 17:51
  • @JACK good catch, yeah. Amazon/Alibaba at it again... – Harper Sep 11 at 19:47
  • @ Harper I'm learning from you guys!! – JACK Sep 11 at 19:52

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