Next time I separate the fender from the inner wheelhouse, I will route and tie the subwoofer feed so that it is concealed within the fender. If you do this, be SURE to fuse it between the battery and the concealed area.

Another reason not to use any existing harness for a power amp is the tendency for the headlights, tail lights, and dash lights to pulse with the beat.

I'd like to see those pics!