nosseemi

Hey!
I have tried for few days now to instal an after market sub to my audi a4 b8 2008 and I ran to a problem. I cant find an wiring diagram for the my system. I have and mmi 2g basic with an cd changer in the dash and a navigation the controls are around the stick. Also I am confused is the cd changer the "radio/stereo" unit or is it some where else bcs behind the cd changer there is only like four wire that come in and in the factory amp there is only 2 wires tha come from the radio if i can trust the diagrams i found online. Also i tried to conect the new amp trought a low line converter to the front speaker wires that are after the factory amp and it caused my mmi screen to shut down instantly after it startet. Anyone have any tips where i can get the singal for the low converter. (also sorry for typos not my native language )