factory alarm question for 1995 mustang gt convertible
 

I just recently bought a 1995 Mustang GT convertible and to me it looks like it had an alarm system but someone took it out. On the window it has an AVS sticker(factory alarm)? Also it has a little red button down by the shifter. I found the connector for the AVS under my dash(drivers side). Is there anyway I can just buy a new alarm and just plug it in? What would I need? Does AVS have a website? Thanks a lot.