Yeah, you need to go buy what's called an Speaker Level Converter. Well let's assume you know how to wire the amp and the subs.
If you have the stock headunit, you need the Scosche Speaker Level Converter, it wires to your two rear door speakers. Then you just run your RCA cables from that Speaker Level Converter to your amp. I would "consider" professional installation. I got everything wired for $50, not to bad.
And if you do not have a stock headunit, I am sure their may be RCA cable connects on the back of your headunit.
$50 for professional installation would be a good deal and I'd take it. Having done a few of these, I enjoy the challenge. What Ryman said is correct, there is no RCA connection on the stock head unit. If you have an aftermarket HU, it's much easier.
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