Originally Posted by Beemer
Tim, can't you simply use a mains switch?
I know that this is an old post, but it's resurrected, and I just want to comment: beware of using "mains switches" in cars. They are not rated for breaking DC. You may get away with breaking an amp or less, but a heater's current requires a DC contactor.
Mains switches get away with being small and cheap because the current crosses zero 120 or so times per second. Not so with DC, and AC-only rated switches could arc and become a fire hazard.