It really depends on your current factory radio.
Does your vehicle have the CD player? If it does, then there are 4 speaker outputs. If you have just the AM / FM radio like I did, it only has 2 channels.
Anyway I have included a picture of an aftermarket harness that has the speaker channels labeled. The 4 channels are in the white / gray / green / purple pairs. The negative is towards the top near the mating release tab.
White/White with black= left front
Gray/Gray with black stripe= right front
Green/Green with black stripe= left rear
Purple/Purple with black strips= right rear