Alarm question

I just got a 99 durango, and the guy I bought it off of said he pulled the alarm siren because he was tired of it going off when he was working on it. Anyhow, I have some extra alarm sirens lying around, and tried hooking that up to the black and red wire that's in the engine compartment where you can see plugged into the old siren. When I hooked it up, the alarm siren was going off constantly, but very very low. I remember I had this problem years ago with one of my third gens, but couldn't remember what fixed it. Anyone have any ideas how to get the siren to work right. It seems like an aftermarket alarm installed using the factory fob. Or if I can't get the siren to work, how can I get the horn to sound off again as an alarm? Any help is appricieated. TIA

Shawn

could be a bad ground for the siren and/or alarm brain. I had a car roll into the shop one time where the siren wounldnt shut off but was really low sounding but it turned out to be the alarm brain was bad.