Make sure that the shower fuse is removed or switched to OFF before you begin. This is essential!
Take the 2 screws out of the switch and it will drop down on its cables. You'll find one brown or red wire coming in from the fuse box, and one brown or red wire going to the shower. These are the LIVES. You'll find the same with the black or blue wires- these are the NEUTRALS.
The green and yellow wires are Earths and you'll see they are connected together.
The switch terminals will be marked L IN (live in from fuse) and L OUT (live out to shower). The other one will be marked N IN (neutral in from fusebox) and N OUT (neutral out to shower). The OUT terminals may be marked LOAD by the way, but I think you'll get my drift.
Hope this helps!
John
January 2008