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I have two light bulbs controlled by three light switches. I replaced two of them a while ago (can't remember what the wiring looks like) with no problems. However, I encountered the following issue when attempting to replace the third light switch. The diagram belows shows the old one on left - the new one, to be installed, on the right :

Wiring diagram of light switches, current on left new one to be installed on right

Any advice on how to wire up the new switch ? The red lines show a connection outside of light switch and earth I have not included, it is also outside of switch.

The two lights themselves are both either turned on or off, ie I can can turn both on at one end of hallway and then walk along to other end (or the middle) and turn both off - they work as intended. But I have no idea how to wire up the new switch, is it even the right type of switch ?

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See my answer to this question What do I need to replace 4 light switches on the same circuit? – Tester101 Dec 12 '11 at 13:22
up vote 5 down vote accepted

That's a 4 way switch, not a 3 way switch (your replacement device is a 3 way). That switch is in the middle of the chain, and you need to replace it with another 4 way switch.

I found a tutorial on 4 way wiring here: http://www.wfu.edu/~matthews/courses/p230/switches/SwitchesTut.html

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+1 for the same answer, I was even going to use the same link! – BMitch Dec 12 '11 at 12:28
my replacement device is called a 2-way on the box, the com hole is for common wires (the two reds) ? – NimChimpsky Dec 12 '11 at 12:29
in fact, I can't see a 4 way light switch advertised anywhere (the high street uk diy superstores) – NimChimpsky Dec 12 '11 at 13:09
@NimChimpsky In the UK they may be called 3-way switches. Either way the switch you need will have 4 terminals (+ground), not 3. – Tester101 Dec 12 '11 at 13:19

In the UK a 2-way switch is used for switching a light from 2 places. It is called 2-way because there the Common terminal is switched to one of two L terminals.

The middle switches with 4 terminals are called 'intermediate' in the UK.

eg http://www.tlc-direct.co.uk/Products/MKK4875.html

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