How to reset radio from security on 1998 jetta tdi?

1) Turn on the radio, "SAFE" should appear 2) Hold down the "MIX" ,"MODE", and "SCAN", all at the same time, for 3 seconds. 3) If done correctly, "1000" will appear. When "1000" is shown, you need to enter the radio code. Enter the 4 digit radio code, and that's it. I'm assuming you are asking this question because you don't have a radio code at hand... there's a few ways to go about this. 1) Code may be on a sticker in the spare tire well 2)You can pull the stereo headunit either with the special radio removal keys or you can make you own using pieces of a credit card. Search a VW forum for more details. The code may be written on top of the headunit. Will usually begin with a 0 or 1. The most hassle free way (but not necessarily the cheapest), will be to visit the dealership. VW is supposed to give you this key free of charge, but this isn't always the case. Best of luck!

If I don't have a code

Radio comes on but, no sound, nothing. Radio comes from a VW Passat. There is no security number on the radio. Bought this radio at flea market. How can I get the security number, besides going to the dealership