I know this has been covered before but could someone link to to the thing that you need for a factory headunit to be able to install and amp.

 

i know that someone knows....

 

You either need an amp with line level inputs so you can connect straight to your headunit's speaker wires or you need an RCA converter to connect to the speaker wires and convert it to RCA.

 

Exactly what Xsi said - but you will sacrifice sound quality by going this route. If this is not important at the moment, then you are all set. If not, I suggest you upgrade the head unit as well so that it sends audio signals via RCA's or even digital (fiber optical for best sound!).