I would go to the fuse box under the dash, and with a voltmeter, find a terminal that is live (12v) all the time. Then using a small push-on terminal lug, connect the phone power to that terminal. That way your phone is always powered up even with the ignition off. If you don't want to leave the phone powered all the time, just look for a terminal that is live only when the ignition is on and when the key is on acc.

Sounds like you already found a good power wire but the best installation would be to wire it directly to the fuse box.

Hope this helps....