I have this 1999 A4 1.8. The factory stereo was removed by the previous owner and they put in this aftermarket stereo. the lighter fuse was not in place. I put one 20amp fuse (it requires a 15amp) and it blew right away. I tried one 30amp fuse that blew too. any idea what's going on?

 

Most likely you have a short at the cigarette lighter.

Try taking off your trim and disconnecting the lighter and see if it still blows a fuse. You can then take a volt meter and check for a short at the lighter itself if the fuse doesn't blow when the lighter is disconnected.