Dimmer switch help

Hi, I am replacing a single light switch that controls one light with a dimmer switch, I\\\'ve mixed up the labels and need some help to get it working properly please !

The dimmer switch has common, L1 and L2 terminals and I have two white wires coming from the wall each containing 3 copper coloured wires - black , red and one with no plastic cover. I put both blacks in common and both reds in L1 and the light came on but wouldn\\\'t turn off ?! Every other combination I have tried hasn\\\'t worked either.

Does anyone know which colour wires should go in which terminals ?

Any advice gratefully received !

This sounds like you've actually bypassed the switch, which ought to be in the live part of the circuit. I assume you don't have a voltage indicator?

If you have a voltage indicator (mains tester screwdriver [nasty things] neon 'volt stick' multimeter...) separate all the wires, turn on the power and check which one is live. It should be one of the red wires.

If it is and no others are live, do this: Connect one red to Common and the other to L1. Then connect the two black wires together with a connection block (separate from the switch terminals) and connect the two bare wires to earth - they should be sleeved with green and yellow sleeving - there may be an earth terminal on the switch, otherwise there should be one on the galvanised box set into the wall.

BUT, if in doubt, leave it alone and call in a sparky. (And if you haven't got a means of detecting which wire is live then you WILL be in doubt)