you need a line out converter like this
http://www.amazon.com/PAC-SNI-35-Variable-Line-Converter/dp/B001EAWS3W
and you need to splice the wires coming from the radio to the corresponding wires from the line out converter. This will allow you to hook up your rca feeds to your amplifier. Your amplifier needs to run off of your car radio switched accessory 12v which is a yellow wire.
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Power Antenna Trigger Wire: N/A
Car Stereo Amp Turn-On Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Tweeter Size:
1″ Tweeters
Car Audio Front Tweeter Depth: 2″
Car Audio Front Tweeter Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Front Speakers Size:
6 1/2″ Speakers
Car Audio Front Speakers Depth: 3 1/2″
Car Audio Front Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue
Car Audio Rear Speakers Size:
6 1/2″ Speakers
Car Audio Rear Speakers Depth: 3 1/2″
Car Audio Rear Speakers Location: N/A
Car Subwoofer Speaker Positive Wire (+): N/A
Car Subwoofer Speaker Negative Wire (-): N/A
Car Subwoofer Speaker Size:
10″ Subwoofer
Car Subwoofer Speaker Depth: 4″
Car Subwoofer Speaker Location: N/A
Hope that helps