hi , i am replacing a bathroom pull cord switch because of a faulty pull switch, the old light has 2 N and 2 L and they are 2 grey mains cable coming from the ceiling each with a black , red and a bare wired i assume is earth , when i took the old switch off the 2 black and 2 red were joined into the 2 N terminals, but the new switch has a L and a COM and every time i try it the fuse blows , i have tried every way i can think of and either the light does not come on or it blows . If i put the old switch back on the light works fine but ihave to loosen the casing down for the pull switch to work which exposes the wires . someone please help cos i am completely stuck. ta luca