Do it once and do it the right, easier way.
I started by buying an amp with line level inputs and wired it off of the amp output. Worked great until stock speakers self destructed. I then **** canned all stock RF equipment including speakers and ran all new wires for speakers, 3 way active up front, components in back and modified stock sub box so 8" sundown audio sd4 would work. Sounds super wasn't hard to do after getting rid of stock wires, which are a nightmare to work with. Ditching stock may sound bad but if you want any quality ou have to, the RF system is better then stock radio but is still junk. Buy a five channel amp, speakers, head unit of choice, a JL audio W3 8" 4 ohm dual voice coil will work with stock sub box great, maybe not perfect size but just make a new front same width and height of stock box, cut hole for sub in it and mount to stock box and cut plastic out. Run your cable, fill it lightly with hollow fill and mount your sub. Fits perfectly under seat. It's a little work but if your going to take on screwing with factory wiring it's a lot less work, head ache and time. I did it the hard way first and wish someone told me to shitcan everything before you do a thing because no matter how you do it, it's going to still sound like ****, just better. You won't be happy with results until it's all out of there and replaced with quality equipment, which if you do your homework can be had for a few hundred bucks if you wish or a few thousand. The cheapest name brand head unit out there when hooked to a name brand amp will be miles ahead of your stock stereo, and you still can have all of your steering wheel controls also. I didn't do much homework or research and had to take first grade over again, learn from my mistakes. Once you start, there's no stopping. Do it once and be done. Here's a couple pics of sub during experimentation and final product.
