1991 Cadillac Seville

Let's go back to square one. You had a no start with a presumed wait three minutes message on the info center. You determined it was an ignition cylinder, and bypassed it, how? Why was the vats module replaced? Many possibilities exist, do you have they correct value key to module(there are about 15 variations). You did not need a vats module if it was determined you had a failed cylinder. Have you tried the old module with the cylinder bypassed. I am going to need more info on what has been done specifically, and why. If you had a failed cylinder, and you knew the correct value of your key pellet, you could have plugged a different cylinder in place with a new key, tucked it under the dash, and that should have bypassed it and allowed it to start. Currently, does the theft message still display?, if not has the signal to the starter been checked and verified absent?

thanks so much for your quick reply
when the car was purchased used, the dash readout read anti theft system activated the car may not re-start
although it did for about two months
did a turn up spark plugs, wires, filters and oil. I disconnected the battery to replace a cable end. the car would crank but would not start after i replaced the cables. i tried to reset the system using the door locks (both) they appear to work as i get the wait 3 minute message after doing so. i tried leaving the key on for 30 minutes and several other "reset techniques " suggested then i learned of the lock cylinder problem. it was bad.
had the key pellet checked with the dealer, a key shop and with a volt meter it's an #11 at 4750 ohms ideally.
bypassed the ignition lock cylinder with a resister pack of 1/2 watt resistors equal to that value. the display now reads starting system disabled due to vehicle anti theft system remove key. and then reads wait 3 minutes. then start car. when attempted the car tries to start for a split second then won't and the whole process begins again.
I replaced the vats module on the advice of the dealers mechanic. i am getting 5 volts dc at the output for the vats module. drops to 3.29 with resistors installed. wiring harness and connectors to module and ecm appear to be in good shape, since the car was running when pulled in the shop i am assuming that wiring connection is not the problem.
re-set the computer and cleared codes before hooking up new module installed it as per the directions provided. still get the same conditions and read out.
any help you can offer would be greatly appreciated
Don

So, the value of your resistor pack is 4750 ohms, this has been checked with an ohmmeter? I still think that you have a problem in that area, unfortunately I can't see the car. My suggestion would have been just to get a cylinder and key and put it in place. Considering that is where your problems began, and it was confirmed as the failed part.