I curerntly have (I think!) 2 2way switches, 1 on the landing operating the attic light independantly and 1 in ther attic doing the same. I want to replace the switch in the attice room from a plastic switch to a metal dimmer switch. On the original there is a C, an L1 and L2. On the new dimmer there is an L1, L2, an earth and another symbol that looks like a switch symbol. I have a red, blue and yellow wire - any suggestions. PS - appears to be no earth wire!