All cars were positive ground at one time including american cars. I haven't converted a car but I did an old tractor. The only thing I had to change was the charging circuit. Remove the generator and replace it with an alternator and, of course reverse the battery. You can hook up a stereo in a pos gnd car but you have to be extremely careful not to groung anything on the stereo. The chassis would have to be connected to the hot wire (neg) from the battery and the 12v connection from the stereo would have to be connected to the car chassis. Also be careful not to ground any of the speakers.