There was no factory alarm system, however there was a Ford branded, dealer installed, alarm system made by Code Alarm
, which was later sucked up by AudioVox
. I believe they still offer some support for the Ford branded systems.
The control module looks like this:
Here's the description of the connections:
I do not believe it interconnects with PATS but who knows (alarm systems are a PITA).
Your '96 has PATS type A, described as below. There was no PATS starter interlock used on Mustangs until the 2005 MY: