that won't work. the remote wire gets 12V from the head unit, and only shows 12V when the radio is on, not just the ignition. disconnecting the harness from the head unit will make finding the remote wire useless.

there are two schools of thought for the ground. (1) as short as possible and (2) ground everything in the same spot so you avoid ground loops. if you ground it in the trunk and you get a buzz, you have to run it all the way back the battery anyway. that's why i suggested to run the wire anyway, just in case your short wire doesn't work --