New dimmer switch problems

Mr_s

Having been told how easy it is to change a dimmer switch, I thought I'd give it a crack. Apparently it's harder than I expected!
Having a slight issue, my old ligth switch has 3 red wires and the earth wire.
two reds go into common, and the and the other red goes into L1.

The new dimmer switch I have bought has 3 holes. L1, C, and L2.

Only holes l1 and l2 have conductive material + a screw.
C is just a plastic hole.

Should I keep l1 as it is, and put what was in c into l2?

Or should I stop trying to save money and leave it to the pros?

dominoman

I'd put the two reds from Common into L1 and the other red into L2. You don't need the earth unless the switch is metal so just tape it off.

I think the C is for 3-way switching (like in a hall).

BTW I'm not a sparky, though I do do all my own elec work, so do this at your own risk.

TheCyclingProgrammer

More information needed. I'm assuming it's a single gang switch, is it one way or two way? It sounds like a one way but the wiring sounds unusual. How many cables are there? One or two? Post a photo?

The above post is wrong however, a one way switch will switch between the L1 and L2 terminals, the live feed goes to common. The switched wire usually goes in to L1 but either will work. In a two way switching setup the live would go into L1 and switched live L2 and the common is used only as an interlink with the other switch.

If OP has a one way switch then whilst I do not know what the additional common wire is for in that case, logically the new switch should be wired up in the same way. Are you sure the common terminal has no screw? Did you buy the correct switch?