AbRang

I have a new 2014 Se Stock model. It has only 4 speakers one in each door (will be replacing soon). I wana keep the original head unit (for now) was wanting to know how other people have wired thier amps that don't have a factory sub in the back. I'm trying to figure out where I can locate the wires from the back doors maybe run them to a RCA converter and run my amp off that so I can hook up my aftermarket sub. ANY HELP IS APPRECIATED. Just trying to hook up a sub for now.