I am having a problem with the rear speakers in my 2001 audi a4, the
front speakers seem to be fine but the rear speakers seem to play at a
very low volume also I do not think the rear sub woofer is working.

I have been told they work on a seperate amplifier but I am unable to
locate it.

Does anyone know where I can find a detailed wiring map of the standard
audio, or has anyone heard of this problem before?

thanks for your help..