kill switch

What ever you do you need to make it so that it is not obvious what you are doing. Switch in the trunk? If somebody were watching your car and seen you open the trunk it would not be all that difficult for them to get into the trunk to flip the switch.

Same goes for fumbling under the dash or under the hood. Been doing some research this morning and might go with a passive RFID type switch.

Wiring the ohm meter wires effectively turns off all power so the radio will have to be reset every time and that is a pain.