First off, understand that this is the Roadmaster forum, not the Regal forum. However, I believe the PassKey systems are identical.
I have replaced the module with another unit ( not a new one)
Ok, well there's the first problem. The module will memorize the resistance of the first key inserted into it. Forever. It can never be changed again, by any procedure. So there is a 1 in 15 chance that your existing key will work with your used module.
You need 15 resistors, one of each of the following value, +/- 3%:
402
523
681
887
1130
1470
1870
2370
3010
3740
4750
6040
7500
9530
11800
Now, disconnect the PassKey connector under the dash. Connect your first resistor to the body harness (male) side of the connector. A couple of alligator clip test leads may be helpful for this. Turn the key. If the engine cranks, congratulations, you now know the required resistance. Personally, I would wire that resistor in there permanently, but otherwise, now you can get new keys cut with the appropriate resistor pellet. If the security light is tripped and the engine won't crank: "Sorry, try again". After shutting the key off and waiting 4 minutes, of course.
The theft deterrent module has nothing to do with the door locks or the diagnostic connector -- sorry, but you fried some other stuff too. Which probably took more than 16 volts to do. The dead diagnostic connector likely means you fried the PCM too.