The amp is on the driver's side behind the knee bolster panel.
see here:
How To: Access The Factory Amplifier
wire colors here:
FAQ - Audio Upgrades
from the FAQ above:
Note: The the first color is the color of the wire and the second color is the color of the stripe on the wire.
Dash Left +: Gray/Orange
Dash Left -: Gray/Yellow
Dash Center +: Gray/Brown
Dash Center -: Gray/Orange
Dash Right +: Gray/Dark Green
Dash Right -: Gray/Light Green
Front Left +: Gray/Violet
Front Left -: Gray/Yellow
Front Right +: Dark Green/Violet
Front Right -: Dark Green/Yellow
Rear Left +: Dark Green/Tan
Rear Left -: Dark Green/Gray
Rear Right +: Dark Green/Brown
Rear Right -: Yellow/Gray
Subwoofer +: Grey/Brown
Subwoofer -: Dark Green/Brown