Connecting your speakers to an amp. Tip: You can use your vehicle's factory wiring: http://bit.ly/WKQP6h
"Sending a signal from a receiver to an amplifier's input via RCA-type cables or the speaker-level outputs is straight forward and simple enough, but getting the amplified signal back to the speakers—well that's another matter. The speakers are usually in four different corners of your vehicle, and running separate new speaker wires to each presents many challenges, including how to get the wire past the car door hinges to the front door speaker locations. A convenient way to send the powered signal from the amp to your speakers is to run the speaker wires to the harness that’s behind your receiver, where all your car’s speaker connections are accessible in one place."