1997 Cadillac Eldorado Owner's Manual - Page 66

The square key is forthe ignition only. It has a resistor pellet which is part of the vehicle's PASS-K~Y@IT system. When a new CadilIac is delivered, the dealer removes the plug from the door key. The plug has a code on it that tells the dealer or a qualified locksmith how to make extra keys.The ignition key has a bar code tag attached to it rather than a b o c k out plug. Your dealer qualified locksmith can make extra ignition keys by reading the bar code tag. Keep the bar code tag and the door key plugs in a safe place. If you lose your keys: you willbe able to have new ones made using the plug or bar code tag. The oval key is for the doors and all other locks.