The panel from the 1990 model looks different because it mates with the Delco-Loc cassette players with the graphic equalizer of the same year. The "MUTE" button will unlock the radio if necessary. The 1992-93 panels are different in appearance simply due to revision of the part, and their "MUTE" button will not unlock the Delco-Loc cassette player. All of the CD players of the era were Delco-Loc II (user-entered code).