It should only be a matter of making a way of completing or disrupting a circuit.
Mind you, you should always disconnect the negative terminal of your battery for safety, and before you do this do some more research. I'm just trying to give you a better idea here.

Imagine a wire that's always hot (charged or on...)
Cut it, and connect the switch to either end. When you turn the switch to On, then it's charged. When it's off it's disrupted or... off. You may need a relay to keep the switch from getting fried. There may be a fairly large number of amps in that location of yours.