I have a '10 ram 1500 crew with the alpine sound system w/sub. Of course it is flat as a board on the bass so I'm putting a 12' in a vented fox box run off the amp it was previously paired with. My question is how is the factory sub connected? Can I just tap the line before the factory amp and run it to the new amp, or do I have to get a LOC and pull from the door speakers like a normal factory stereo port?