All pin-outs are looking at the face of the connector.
NOTE: There are two kinds of CD changer connectors for pre-99 VWs. One is pink, and one is black. The pink connector is for the panasonic radio (manufactured by Matsushita, with data and RCA connectors at the changer), and the black one is for the Clarion radios (single connector at the changer). These are NOT the same. THe pinout that follows is for the Panasonic radio only.
NOTE: certian US-built models have a different radio conector style then shown here. THey have a black 4 pin connector and then individual plugs to the radio for each speaker. The wire colors shown below still apply.

Main Connector (Black):

Brown/Blue (Alarm) or Blue/White (Vol. Adj.) Alarm or Speed-Volume Adjustment 1 2 Telephone Mute Yellow
White/Blue or Blue/White (AKTIV power signal) AKTIV or K-wire 3 4 Switched Power Brown/Red
White (Power Ant.) or Black (Amplified Ant.) Power Antenna or SAFE 5 6 Illumination Gray/Blue
Red/White Constant Power 7 8 Ground Brown

Speaker Connector (Brown):

RR+ 1 2 RR-
RF+ 3 4 RF-
LF+ 5 6 LF-
LR+ 7 8 LR-

AKTIV Connector (Red):

Data 1 2 Clock
ENA 3 4 -
Speaker Common Ground 5 6 RC
Right Front Line Out + 7 8 Right Rear Line-Out +
Left Front Line Out + 9 10 Left Rear Line-Out +

CD Changer Connector (Pink):

Black Data In 1 2 Clock Red
Green or Black Shield, CD-In Ground 3 4 Data Out White
? Line-Out Ground 5 6 Constant Power Yellow
Red Right CD-In 7 8 Right Line-Out ?
? Left Line-Out 9 10 Left CD-In White

Accessory connectors (1998+):

Amplifier (yellow):
Left Rear Line-Out 1 2 Right Rear Line-Out
Ground 3
Left Rear Line-Out 4 5 Right Rear Line-Out
Amplifier Power 6
External control/display (green):
Open 7 8 Clock
Data 9
ENA 10 11 Remote Control (steering wheel) Yellow/Red
Open 12
CD Changer (blue):
Blue Data In 13 14 Data Out Green
Yellow Clock 15
Red Constant Power 16 17 Switched Power Green
Black Ground 18
Violet CD-In, Left 19 20 CD-In, Right White

Speaker Connector Colors:

Left Front + Left Front - Right Front + Right Front - Left Rear + Left Rear - Right Rear + Right Rear -
1985-1987 Golf, GTI White/Black Brown/White Green/Black Brown White/Black Brown/White Green/Black Brown
1988-1989 Golf, GTI White/Green Brown/Green Green/White Brown/Blue White/Black Brown/White Green/Black Brown
1985-1986 Jetta Brown/Green Brown Brown/Red Brown Blue Brown Red Brown
1986-1989 Jetta, All models 90-99 Blue Brown/Blue Red Brown/White Blue/Green Brown/Red Red/Green Brown/Black

AKTIV Connector Colors:

AKTIV Left Front + AKTIV Right Front + AKTIV Left Rear + AKTIV Right Rear + AKTIV Common ground for door speakers -
1988-1989 Golf, GTI Green/Black White/Black - - Brown/Yellow
1988-1989 Jetta Blue/Black Red/Yelllow - - Red/Black
1989 Jetta, All models 90-99 Blue/Brown Blue/Red Green Blue Red/Black