I see you have helped quite alot of peopl I have just bought a 1999 audi a3 and there was no unit just wires and connectors.
I found this picture I do not have the large brown connector or the smaller yellow and green ones... the black one which succesffully powers my sendai head unit and I have the small blue one and I also have the red and small brown one which I think are not important... I also have 9 loose wires maybe some of these are from the connector things im missing? think standard system no amp on the right so probably have standard amp in sub which is there. Do you know how i;d go about sortin the 9 loose wires or simply just getting sound to my front and rear speakers + sub ??? I have bought pc9-404/pc9-410 not completely sure which ones which though came as multi pack halfords.... any help would be great mate