A light switch got broken the other day (white plastic type) so I went out and got a nice chrome one to replace it. OH ripped off broken one then looked at the wiring and refused to touch it! There is a white wire in there and he doesn't know what its for. HELP!!!! I will soon be paying an electrician to do this 'cos I am fed up sitting in the dark!!
Basic process is to check where everything went on the thing you remove first, and make a note if necessary, so you can connect the new one the same way.
White wire eh ? Colours can vary depending on where in the world you are. You may get a clue as to what is at the switch by checking what is connected to the light fitting.
With any luck, as EDDIE said, there'll be only 2 wires which connected means light on, and disconencted means light off.