If you run 12v constant it will always be on. When I did mine on my 06 I tapped the towing harness for the reverse light but you need to tap the reverse wire to the deck as well. I ran the wire all the way back from there with the rca. There is a post somewhere on here you can tap a wire under the dash would be way easier (I couldn't find it) for the deck. I had an amp under my back seats I used power right from the battery, but used a relay and the remote wire to turn it on when the head unit came on. It worked.