1986 BMW 528 Stereo

actually your radio has an antitheft system to prevent thefts to use it, but most of the times the previous owner will know the code or he might wrote it down at the owners manual,
or you can try to contact the dealer some times they will be nice and just give you the code, but you nned to be ready with the vin number of the car, and the serial number on the radio in order to get the code from the dealer, but if you have a friend or relative with auto repair, they wiil call the dealer, in most cases they have very good erlation with auto dealer.