I will preface this by saying that I have a 1999 with the Mach System.So here goes.

You need the premium amp integration plug from metra. It will have a gray rectangular shaped plug that has the power, switch power, dimmer wire and amp turn on. It will also have a square black plug that has 4 RCA connectors. You can use the one that has the speaker wire connections coming off of the black plug, but if you do you will be running an amplified signal into your factory amp and will have a fairly good chance of distortion.

Also, you do need to put a resistor on the amp turn on wire to prevent it from popping when you crank your car. The popping is an annoyance that you may be able to live with, but if you leave your radio on a high volume when you do run the chance of blowing a speaker when pops.

You also want to make sure that you buy a headunit with pre-amp outputs for both front and rear channels. Some of the cheaper units will only have one set of outputs, in which case you will not be able to fade your speakers from front to back in order to equalize the sound.