just as a point of fact. try not to think of DC voltage as 'ground' and 'live'. this only ends in confusion. in cars, yes there is a ground (or earth). this is negative and is purely there to save on wire. whereas 'ground' in house wiring implies that wire that runs voltage away from you if there is a short. this type of 'ground' has absolutely nothing happening most of the time.
instead, just think of DC in terms of positive and negative. just like on a battery (which of course is a store of DC voltage).
and as markrvp says, a switch isnt polarised. its just something to join a circuit together so it doesnt matter which way its connected...