Well I have dealt with this just recently. I have a car that you need to remover nearly the whole dash to change the stereo or hook things up to it. At your local wal-marts the sale a little box for about 12 dollars. it converts regular speaker wire output to rca for your amp. I bought this and simply took some speaker wire, and put it in the slots of the factory clip that snaps onto your back speakers, ran the wires to the little walmart box and then to my amp. chap and easy, took about 10 minutes. then ran all my power wires, one to the battery, and the rto (remote turn on) to a simple fuse in my fuse box. time from factory sound to thump, approxametly 30 minutes. Also, this works because if I ecer sell the car it still has lot value seeing as no factory items were messed with. still 100 % original.

You can either spend the money and buy a box that will convert your wiring for your ragular speakerwire so the you can send rca jacks or (if you haven't already bought a amp) go ahead and buy an amp with high level inputs already built in. Buying the amp with it built in will save you money and time! Also, the hook up is made much simpler this way. The hook up is just + to +, and - to - . Pretty simple! Also, if you don't know or haven't hooked on up the remote wire for almost all cars is blue which you can run into behind your head unit but if you aren't sure the remote wire should be listed in your car manual!