Car Stereos: not installing aftermarket, chevy trailblazer, channel amp

Question
i'm keeping my factory 6 disc changer for my 2007 chevy trailblazer it has a factory amp as well. im trying to hook up subs i have all my wires ran and my aftermarket amp is ready. I can not figure where to hook up rca converter. tech at best buy gave me wire colors and i verified them on google but the wires behind my 6 disc changer did not match up. i could try the speakers or the harness to the amp but im worried about feed back. can u please help me. every place in town here wants to charge 80 american dollars to tell me or show me. would like to do this myself for the knowledge and future installations. i have a lanzar 15D ported box  with a S.A.G.A 5 channel amp i just purchased yesturday from a private owner withthe estimate of 1600 watts. how will i hook this rca out put converter up to my disc changer. any help you can give me would be greatly appreciated

Answer
Hi Steve,

I don't know the colour of the speaker wires off the top of my head.

What I would suggest would be to tap the speaker wires going into the doors themselves, and then run those leads into the trunk or wherever you've mounted your amp. Then you can be sure you're getting a speaker wire signal.

Justin