Replacing switch

[Bluesland]

I have just moved into a oldish house. The two-way dimmer switch on the landing was not working, so I took off the old switch to replace it. I found a red and black wire into L1, a single red wire into L2, and black and blue wires which looked as though they used to in Com.

I joined black and blue and put them into Com - the result was that I could turn on the light from dowstairs or from upstairs, but I could only turn the light off from the original point - i.e I could not turn on downstairs and off upstairs. I assume therefore that only one of these wires goes into Com and that the other goes into L2??

How to I know which one goes into Com (presumably this will be the permanent live)?, and does the other one go into L2?

Any help would be appreciated.

Thanks

 

[pdcelec]

You need to stop assuming things and use your multimeter to find out which cable goes where. Remember that electricity is dangerous and should not be tampered with willy nilly.

 

[Lectrician]

Odd combination of colours there.

Can you remove the other switch for this point (assuming 2way??), tell us what colours are connected where in that one.

In the switch you are changing, tell us which cores/coloures are from which cable - a cable is a collection of cores with in an outer sheath.