Another popular way to connect an amplifier to a factory radio is to use something called a line output converter. It connects to the factory radios speaker wires and converts the speaker-level signal to a preamp-level signal. This lets you use RCA cables to run that signal to your amplifier.
How do I hook up an amp and sub to an aftermarket radio?
1:1614:22How to install an amp and sub in your car | Crutchfield video - YouTubeYouTubeStart of suggested clipEnd of suggested clipWe had an aftermarket stereo that stereo would have RCA preamp outputs already on it that we couldMoreWe had an aftermarket stereo that stereo would have RCA preamp outputs already on it that we could use you know connect RCA cables directly from there run them to the back.
Do you need an amp for a sub?
Why Do Subwoofers Need an Amp? Subwoofers are designed to reproduce low-frequency sounds. This takes a lot of power. The types of subwoofers that need an external amp to work are known as passive subwoofers, while those that can function without an amp are known as powered or active subwoofers.