Look at the iso plug on your car and just match the pin number to the wire colour.
2000 Volkswagen Golf Car Radio Wiring Schematic
Car Radio Battery Constant 12v+ Wire: Plug #3, Pin #7
Car Radio Accessory Switched 12v+ Wire: Plug #3, Pin #4
Car Radio Ground Wire: Plug #3, Pin #8
Car Radio Illumination Wire: Plug #3, Pin #6
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Plug #2, Pin #5
Left Front Speaker Negative Wire (-): Plug #2, Pin #6
Right Front Speaker Positive Wire (+): Plug #2, Pin #3
Right Front Speaker Negative Wire (-): Plug #2, Pin #4
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Plug #2, Pin #7
Left Rear Speaker Negative Wire (-): Plug #2, Pin #8
Right Rear Speaker Positive Wire (+): Plug #2, Pin #1
Right Rear Speaker Negative Wire (-): Plug #2, Pin #2
Signal for Anti-Theft Alarm System Wire: Plug #3, Pin #1
Data Link Connector (DLC) K-Wire: Plug #3, Pin #3
Battery Supply Constant 12v+ Wire for Anti-Theft System (SAFE): Plug #3, Pin #5
CD Changer Data In Wire: Plug #1, Pin #13
CD Changer Data Out Wire: Plug #1, Pin #14
CD Changer Clock Wire: Plug #1, Pin #15
CD Changer Constant Battery 12v+ Wire: Plug #1, Pin #16
CD Changer Control Signal Wire: Plug #1, Pin #17
CD Changer Ground Wire: Plug #1, Pin #18
CD Changer Left Line Out Wire: Plug #1, Pin #19
CD Changer Right Line Out Wire: Plug #1, Pin #20