The original radio no longer works. Is it possible to just buy a modern Sony or whatever at Best Buy and replace the old one, or is this more challenging due to wiring compatibility or other issues? Thanks.

 

i replaced the stock stereo in my '93 90 with some effort. what i did do is cut the wiring harness and solder the connections. One main difference, i ran exclusively through amps and rewired the entire speaker wiring and speakers. I don't know if the 100 is like the 90 but watch out for rear speakers with built in amps. They'll need some sort of low level input not speaker level input to work properly. the 12 volt website helped quite a bit for determining wires http://www.the12volt.com/installbay/...eard/Audi.html