I just repaired my 97 Eldorado starting problem today. I choose to insert a resistor that matches the pellet value in my key. You can go to Radio Shack and purchase an inexpensive volt ohm meter and use it to measure your key pellet. Then purchase a resistor that matches the value. Use a 1/4 watt fixed resistor or if you cannot find the exact value then purchase a variable resistor trim pot and adjust it to match your key pellet value. I used a 10 turn trim pot adjusted to a 2.33 kilo ohm value. Someone at the store should be able to help you with this.
You will need to remove the cover under the steering column. Mine has a decor cover with a metal cover under it. Once you have all of that out of the way, :worship: locate the large multi-pin connector next to the column. Locate the 2 wire orange wire harness which should be in positions 12 and 13; they are the last two on that row. Positions 10 and 11 were empty on my wiring. Cut the orange wire harness about 3 inches from the large connector. Strip about 1/2 inch of insulation from the ends and solder or crimp the reistor so that it bridges between positions 12 and 13 on the large connector. The resistor should now be the only connection between 12 and 13, do not re-connect the wiring that goes to the ignition key switch. The engine should now start when you turn the key. Insulate and tie wrap the resistor. I tie wraped the resistor to some of the other wires to keep it from flopping around.
Your anit-theft system will no longer function but at least the engine will start.