Im pretty aware this has been asked loads of times, so im going to lay it down as iv understood it. Iv been told by a local audio shop that i will need at least 2 different harness to make the steering wheel work with the radio and then the rear speakers and sub with radio. Iv read a few pages and how i see it is... Obv need to run a power cable through car. I need to ground the system. I need a remote (i will have to check radio schematic) Next would be the the new sub itself, I have no RCA on the back of concert II so i would have to tap into the wires connecting to the standard sub? As for amp id need to find a way to also connect it to the rear speakers, aswell as the sub? I really dont want to have to take this to autosounds as theve quoted me around 450-800 depending which option i go for. (this is without me buying the sub/amp and wiring) someone point me in the right direction and id really appreciate it. Chris. EDIT, i have a 56 audi a4 b7 with concert II + built in sub.