I recently got a RF p4004 4chan. Amp for my car and I'm looking to hook up a sub or two. My question is how can I hook this up. I have run all my amp wires (Bat. remote, ground) but the only input I have for my amp is a pair of RCA cables. I took an old cable and cut the terminals off one end exposing the raw wires and combined them with the speaker wires from my rear speakers for the input signal. When I went to plug into the amp, the sound from my rear speakers drops. Also, my sub I have hooked up doesn't get the correct imput and will just run constant and not to the beat of the song. Ideas and suggestions would be greatly appreciated.

Newer headunits are so cheap nowadays and so many outputs and settings. Why not just update what you have rather going through all this?

You need one or two adapters such as this: Boss Audio B65N Multimedia Accessories - Video/Multimedia at Onlinecarstereo.com

The sub generally needs to be allowed to respond to low frequencies. Can be done in the AMP. Best way is to use a dual voice coil sub and a stereo amp with the low pass filter. Lots of options.

The car is a 04 camry XLE with a jbl sound system and 6 disk CD changer already from the factory with a woodgrain faceplate so its pretty difficult to remove and I was only able to take a peek at the back of it to look. The sub and amp were a friends who was getting rid of stuff cheap so I got a RF p4004 and a Punch p3 15" sub for 50 total. Made a custom sealed box from parts at home so for a cheap setup I wasn't concerned with changing the head unit or any other stuff. Going to try the converter and see how it goes.

Another question / point is that when I split the signal from my rear speakers to my input my speakers aren't nearly as loud as they were and I'm thinking its due to loss of power since the signal is now being split. Thanks for the answers and ill post with an update soon.

RCA Audio Signal Splitter Amplifier distribute 5 Output - eBay (item 220561906072 end time Mar-26-10 04:02:45 PDT)

The factory JBL system on the '04 Camry XLE has a separate amp. And it's marked 'JBL'.
I believe it's located behind the glove box. If not, only one other place... and that would be under the pass seat.
FYI... the heater control faceplate pops out with 4 claws holding it... easy!
Then the radio bezel (wood grain) pops out after that. Total radio removal time is like 5 min.
That's... if you need to get back there, but I don't recommend messing with it.