This is for a 98 but if the radio or body was not changed then im guessing that this wiring diagram should match up to the 03. im 70% sure though so dont count on it.
Radio Constant 12V+ Wire: Orange Radio Switched 12V+ Wire: Yellow Radio Ground Wire: Black Radio Illumination Wire: Gray Dimmer Wire: Brown Antenna Trigger Wire: Pink Front Speaker Size: 3 1/2 Front Speaker Location: Dash Left Front Speaker Wire (+): Tan Left Front Speaker Wire (-): Gray Right Front Speaker Wire (+): Light Green Right Front Speaker Wire (-): Dark Green Rear Speaker Size: 6 x 9 Rear Speaker Location: Rear Deck Left Rear Speaker Wire (+): Brown Left Rear Speaker Wire (-): Yellow Right Rear Speaker Wire (+): Dark Blue Right Rear Speaker Wire (-): Light Blue
Radio Ground black - radio harness Radio Ignition (Class 2 Serial Data) Radio Illumination gray (dimmer) + radio harness Factory Amp Turn-on pink + radio harness or amplifier Power Antenna N/A LF Speaker +/- tan - gray +,- radio harness RF Speaker +/- lt. green - dk. green +,- radio harness LR Speaker +/- brown - yellow +,- radio harness RR Speaker +/- dk. blue - lt. blue +,- radio harness