Hi all. I have an Audi A3 2008 TDI. I have purchased z new stereo for it and ordered a quadlock to iso connector for it. The old stereo was a Concert with mp3 capability. After connecting the new lead there is no sound from the rear speakers. The new lead doesn't have the same amount of connections on the quadlock as the original. Has anybody else had this problem? If so how do I sort it. Thanks