that would be the alarm ECU

 

When I turn ignition to position 2 I get a rapid clicking sound and the engine won't turn over. I suspect the alarm ECU is kaput?

 

Normally a rapid clicking sound is the starter solenoid. Of course it depends on where it is coming from. Low voltage usually causes this.
I would check out the voltage on the battery(maybe try another battery) or check out the starter itself. Just some thoughts, mind you.
edit: just saw where you said the rapid clicking was on position 2, not on the starter position.