Aftermarket stereo

[Baysideautos]

Hi I bought my first Audi it had a aftermarket stereo which i removed and gave back to the previous owner it had some kind of adapter fitted since removing the stereo and fitting my own. I have power to the stereo but no sound. I found a random blue cable in the boot i traced back to the stereo adapter where is it meant to go?

 

[Erikn89nl]

Blue cable is probably the +12V cable for the stock amp. Is the stock sub still there? it has the amp for the rear speakers built-in I believe. Also makes a difference if the car has Bose system or not.

 

[Baysideautos]

The car does have a bose system the sub is still there