This is what Audiovox lists:
#506762: 2005 AUDI A4 2DR CONVERTIBLE
Audio/Mobile Video
WIRE COLOR POLARITY LOCATION
Battery RED / WHITE (+) RADIO HARNESS
Accesory BLACK/ BLUE (+) RADIO HARNESS
Ground BROWN (-) RADIO HARNESS
Illumination GRAY/BLUE (+) RADIO HARNESS
LF Speaker (+) BLUE/WHITE
LF Speaker (-) BROWN / WHITE
RF Speaker (+) RED
RF Speaker (-) BROWN / RED
LR Speaker (+) BROWN / WHITE
LR Speaker (-) BLUE/WHITE
RR Speaker (+) BROWN / RED
RR Speaker (-) RED
Steering Cntrls
THIS VEHICLE MAY BE EQUIPPED WITH OPTIONAL ONSTAR® TELEMATICS EQUIPMENT. USE AN APPROPRIATE INTEGRATION HARNESS OR INSTALLATION PROCEDURE TO ENSURE PROPER FUNCTION OF THIS EQUIPMENT.
Radio Security YES
Security
WIRE COLOR POLARITY LOCATION
Battery RED (+) IGNITION SWITCH HARNESS
Ignition 1 BLACK (+) IGNITION SWITCH HARNESS
Starter 1 RED / BLACK (+) IGNITION SWITCH HARNESS
All Door Trigger BROWN / WHITE (-) IN HARNESS IN DRIVERS KICKPANEL
Trunk Trigger WHITE/ BLACK (-) IN HARNESS IN DRIVERS KICKPANEL
Parking Lights GRAY/BLACK (+) AT VEHICLE LIGHT SWITCH
Convenience
WIRE COLOR POLARITY LOCATION
Headlights-Lo WHITE/ BLACK (+) AT VEHICLE LIGHT SWITCH
Remote Start
WIRE COLOR POLARITY LOCATION
Battery RED (+) IGNITION SWITCH HARNESS
Ignition 1 BLACK (+) IGNITION SWITCH HARNESS
Ignition 2 RED (+) IGNITION SWITCH HARNESS
Accessory 1 BLACK / YELLOW (+) IGNITION SWITCH HARNESS
Starter 1 RED / BLACK (+) IGNITION SWITCH HARNESS
Anti-Theft Type UNIVERSAL IMMOBILIZER
Anti-Theft Descript THE KEY SENDS AN RF SIGNAL TO THE BCM MODULE THROUGH AN ANTENNA LOCATED AROUND THE IGNITION CYLINDER
Tachometer GRAY (AC) AT IGNITION COIL
Speed Sense WHITE/ BLUE (AC) ABS MODULE
ABS CONTROL MODULE LOCATED ON DRIVERS SIDE FIREWALL. PIN 33
Parking Lights GRAY/BLACK (+) AT VEHICLE LIGHT SWITCH
Brake Lights RED / BLACK (+) AT SWITCH ABOVE BRAKE PEDAL
Modules
WIRE LOCATION
Please select another category
Doorlocks/Windows
WIRE COLOR POLARITY LOCATION
Power Unlock RED / BROWN (-) IN HARNESS IN DRIVERS KICKPANEL
PowerLock GRAY/WHITE (-) IN HARNESS IN DRIVERS KICKPANEL
Note: Audiovox makes no representation or warranty with respect to the above information including its accuracy, completeness, or its freedom from third parties' proprietary rights. Audiovox disclaims all liability or responsibility for errors or omissions therein or any decision made by the recipient in reliance thereon. The installer must verify any circuitry with the proper test equipment prior to installation.