1998 Cadillac Deville STARTING DISABLE MESSAGE

More than likely the ignition cylinder is the culprit. The wires that carry the key resistance value out of the column are very small, and over time break. One way to check this is, under the left side of dash, there is a large connector held together with a 7mm bolt. This is the column connector. In one of the thin flat side connector bodies is a larger orange conduit with two small white wires in it, those are the wires. Disconnect that connector, and with an ohmmeter, probe the wires with the key in the cylinder. If you have resistance, something other than infinite, then rotate it in all ranges. You could have opens at run or crank, and not in off. Compare the value with that of the key. Remember that your body has resistance, and will affect your readings. The reason I say that, is the key pellet is difficult to measure without using your fingers, and that would affect your readings.