I have the Factory Mechanics DVD and it only shows the anti theft pats system. Does not talk about or even mention an alarm. I think the harn blow you hear when you lock the truck is to let you know it is locked.
I have a 1995 F-150 XLT 2 wd ext cab i locked the doors today cam back opened drivers door lights fashed horn started blowing. Would nt quit for 1 min or so. Finaly stoped and truck would not start said CK ENG. Trided unlocking and locking drivers door nothing finaly tried pass door everthing started working. Now i am tring to find out how to disable the dam thing. So if your truck says theft i red letters i bet u have same system this thing has.