Review on Enhance Your Car Audio with Crux SWRAD-55 Radio Replacement Accessories by Norman Costello

I bought this wiring harness to fit an Audi A4 B7 without Bose. The problem with this setup is that from most reviews the amp seems to be expecting 6V line-to-line, while most head units supply 2V. So, once installed, your head unit is most likely providing the correct output to the speakers. However if you connect the line out to the factory amp for your rear speakers you will get a very weak signal as the amp is expecting 6v but your main unit is supplying 2v. There are other harnesses that will provide the 2v to 6v boost required for the preamp, but this box will not do that. So be careful when buying one, as the B7 and similar setups don't work by themselves with standard non-Bose hardware. This should have been done with a warning/advice that it would not work with all Audi vehicles or even the vehicles it was designed for.