I would say wire it too the ignition on side of the switch and this is why .
1 Not only would the battery be isolated automatically, the circuit would be
locked out when the key is removed, redundant battery isolation.
2 It would auto isolate the battery when the ignition it tuned
off, by dropping the path to the relay. Making the procedure of start
up, two functions, key on and the press button to activate the battery
isolation relay .
Remember that 2007 has a few preset or memorized items. When batteries are replaced in the newer style cars there are items that are reset to a base standard when all the power is removed . Clocks, computer engine mapping, oil change alerts, these types. So it just might not be a good idea to isolate that battery like you have in mind. Before computer monitored cars came along the only remembered function were a few preset radio stations .. not the case in todays cars.
Last edited by pepi; 05-03-2010 at 08:09 AM.