how do i enable dealer karr 4040a

I recenty bought a mustang from a dealer. All these cars are fitted with the Karr 4040a for security on the lot. When I bought it , they said I could buy it for $500. I said 'no thanks'. They then disabled the alarm but did not remove it. They disabled it by removing a small module with an led , and replacing it with another small plastic module. Both these modules clipped into a  little holder that has 3 wires running to it that they had mounted under the dash on the driver's side.

Having read the installation / wiring details on another post here, I have to assume this is not rocket science. Can anyone out there help me reenable the system, or tell me what the modules do?

thanks

The guy who did the final checkout with me said it was a 4040a and even gave me the little user manual. However , I do believe you , as I cannot see in any of the other descriptions wiring for the module thingy.

Any idea what it could be - I still assume it is a Karr as it was installed by Southwest dealer services (there is a guy who works on the lot)