I have a 97 A4. I hooked up the aftermarket wiring harness like it said to. The green/yellow/blue plug does not get hooked up. The new stereo works, but I have no rear sound. A guy at best buy told me I have to figure out which of the wires out of the green/yellow/blue plug the are. Please help. Thank you in advance.

 

i believe the yellow plug of that green/yellow/blue block are the rear speakers. however you'll need a module to bypass the signal to the rear since the a4's rear speakers are powered and would not utilize your head units amplification. hope this helps.

 

Metra makes a harness for the plugs in question, if you can get some use them. If you are not able to get one its really easy to integrate RCAs. If you look on top of your OEM headunit it will tell you what you need, it will show you which wires are left, right, common and amp turn-on. Strip the signal wires you have found and solder on RCAs,then just plug in your rear RCAs coming out of your aftermarket headunit. If you did everything right you should be good. But if you did not understand then get the monkeys at best buy to order you the plug.