So just to be clear, I am not particularly electrical or mechanical minded...but if something is explained simply enough, I can usually follow along. So, to start:

Tuesday a.m. my car wouldn't start. Heard absolutely nothing out of the engine. Dash lights, radio, etc. would come on. Had it towed to my mechanic (local, non-dealership). He figured out soon after that the security system was complaining. Tried my spare key with no change. So he began troubleshooting. He was able to start it by crossing some wires or something...I don't know which ones or what...but they believe the problem is the BCM and not the ignition lock. No one around has a new BCM apparently - it would be a special order so apparently wouldn't get here until sometime next week. My mechanic says he has found 2 used BCM's locally and is going to pull them tomorrow to try.

Now for the question :>

From the reading I have tried to do tonight, is it true that a used BCM very likely will not work for me due to the fact that the "resistance" it is programmed for will not match my keys? There are about 15 different "resistors", right?

So, if we order a new BCM, then the first time we insert my key it "learns" the resistance it needs to know?

On a very simple level am I understanding some of this right?

FYI: 2000 V6 Manual

eta: sorry, meant to do this in the V6 area.

 

From Alldata

Any new BCM will automatically program to the resistance of the ignition key being used at the first ignition ON cycle. This can only be done once for the life of the module.
The BCM can only be programmed to one ignition key resistance. All ignition key resistances must match.
A new BCM is not programmed. Before the system will function properly it must be programmed to the code that matches the customer's keys.


Insert one of the customer's keys into the ignition cylinder and turn it to the ON position. Start the engine at this time in order to verify system operation.
Observe the SECURITY indicator lamp for the following conditions:
The indicator lamp lights steadily for approximately 5 seconds and then goes out. This indicates that the BCM is programmed properly.
The indicator lamp flashes at a rate of one flash per second until the ignition is turned OFF. This indicates that the BCM did not program and the system should be checked for a fault. Refer to Diagnostic System Check - Theft Deterrent in Theft Deterrent.

This means that if a used BCM is used, it cannot be reprogrammed to your keys. You will need to get new key blanks with the resistor pellet to match the BCM and then cut the keys to fit your ignition switch

 

Thanks for that data...helps me understand. Most likely, I'll be moving my car from my regular mechanic to a dealer tomorrow. My mechanic has done my clutch and other work, but apparently what is going on now is too much for him. The electronics/computer/VATS is too much for him.