I have a manual for a '99 model - the one with separate radio/cassette and CD model No's;
OK55Y 66 860
OK55L 66 860
OK55D 66 860
3K55L 66 860
2K55D 66 860
3K55Y 66 860
Under "How to enter your password"
1. press power button & "Test" appears for 5 seconds, and blinks for 5 minutes. If you turn the power button off then back on again within 5 minutes "Code" blinks on the display.
2. enter password using the numbered buttons - press button 1 once to let it know it's the first digit, then press button 1 again however many times to bring up the code for the first digit. Press button 2 to let it know it's the second digit, then again however many times....etc. To enter default 1111 code, press button 1 twice,, 2 twice, 3 twice then 4 twice.
3. when all four digits entered (default is 1111) press SEL button and display should say "GOOD"
4.You get three goes, if still wrong after third attempt "HOLD" then you have to leave it for an hour
hope this helps