Ignition - alarm interface

So, this truck… Realized some time ago that I couldn’t get the tranny out of park (automatic) and the reason was connected to the ignition core for the key. I replaced the core. When I re-connected the battery, even with the key in the new ignition core, the alarm sounds, and I cannot get the truck to start with the key. Help? I’m going deaf here…

Is this a factory or an aftermarket alarm system? If it’s a factory system see a knowledgable independent mechanic. If it’s an aftermarket type have the mechanic remove it. Aftermarket alarm systems are almost always…junk. They will cause the problems you are having as we speak.

It is a factory alarm system. I was hoping I could figure it out myself, as the nearest mechanic is a five hour drive from the house, and I can’t drive the truck there because it will not start- it would be a very expensive tow!