Some Audi Symphony and Concert radios are NOT prewired for a CD changer.
In such vehicles, a solid 20-pin connector block access to the 8-pin CD changer port.
In order to access CD changer port you will need to use GROM part # AUDS. This harness will allow you to get the access to the CD changer port.
You can read more about the installation into AUDI using AUDS cable here
You can also perform the installation without buying the AUDS harness
Here are the basic instructions how to connect the GROM adapter or any other aftermarket device with the 8 pin connector (blue) to the back of the AUDI stereo.
In order to connect GROM adapter into AUDI where a solid 20-pin connector block access to the 8-pin CD changer port you will need:
1. Get the stereo harness connected at the back of the radio
2. Cut the 8 pin part on the left side of the harness as shown below
3. Place GROM harness into the open space at the back of the car as stated in Installation Document provided with the adapter
This operation will not affect any function performed by the radio as in most cases the left part of the harness is not connected.
If you do not want to break any of the original harness, you will need GROM part # AUDS harness.