The cassette player in a Cadillac Deville is protected by the radio’s TheftLock system. If TheftLock is enabled and the radio is locked out, the cassette player is also locked out. The only way to unlock the cassette player is to unlock the radio’s TheftLock. Fortunately, if you know the radio’s security code, you can use it to disable TheftLock.
Items you will need: radio security code
Turn the car on but leave the radio off. Press and hold the radio’s “1” and “4” buttons until “SEC” appears on the radio’s display.
Press the “Minute” button and look at the radio’s display. It should read “000.” Press and hold “Minute.” Continue holding “Minute” until the last two digits on the radio’s display match the last two digits of the radio’s security code.