This thread says that you have to bypass the stock amp and replace all the speakers too.

Aftermarket H/U and R.A.P. - Dodge Charger Forums

 

I swear I'm just better off putting the stock headunit back in and saying fukc it. All I wanted to do was tap into the amp turn on but those people are saying it's going to sound like crap and burn up the headunit.... What do I do???

 

Put the stock headunit back in or order the stuff you need to make it work.