I’ve recently bought a Audi A3 1.8t 03 plate and changed the head unit but just realised the rear speakers and built in sub don’t work (not bose) looked online everywhere and cannot find the right loom or anything I need to make it work! Can anyone point me in the right direction please! Thanks in advance :)

Have you tried to rewire it yourself? Just replace each damaged cable individually ? I had issues with mine from someone trying to change the stereo and made a right mess and if the stereo was on the automatic transmission didn't shift up or would slip down gears. A hour with a soldering iron and some shrink plastic and it's back to perfect. 

If you have a Haynes manual you can see what each wire goes to and you should be able to pin point the problem quickly

 

Any chance of a copy of that section? 

I have similar issues, bought a 2002 audi A3 (8L2) 1.9tdi sport (130) 6spd,

no standard audi concert, tho is equipped with half amplified system, I fitted an old unit i had lying around tho when I connected the iso connectors only the front worked? I found a set of phonos already tapped into the loom and found the amps power wire to get the rear speakers working, rear is delayed and doesn’t sound as good as the front? Is this the norm this way? Is there anyway of making it sound better? Or even hear the sub?

aby help and advice would be appreciated