My 1999 Bonneville would not turn over at all. Found that the Anti-Thief protection build into the Ignition Key was causing this problem. What happens is the key has a tiny resistor installed in the key, between the shiny metal parts on the key. The key's resistance is read when put into the switch, compared it the Anti-thief circuitry and if it matches allows the car to be started. If it doesn't match it disables the starter circuit and you are dead in the water. Fix it by changing the switch for $100+ or read the key's resister, usually have dozen standard one's, got to Radio Shack and get a matching one and put the resistor in the circuit (google how to do this but it's easy) and car works again for little time spent and dollar resistor.