So you need ignition hot and not constant +12V... if you use a relay, you can search in the E-box fuse box, that is located on the right side of the engine compartment (by the windshield washer tank). do NOT tap directly to any of the wires there for power - buffer the tap with a relay... use battery constant going to the relay's contacts, and the tapped circuit to the relay's coil. try to not use an automotive relay but rather an electronic project relay that draws minimal amount of coil current (shoot for a radio shack relay with 30mA coil current)

how good are you with small electronics projects? can you wire a relay?