I have a writeup in my sig on alarm installs. As for the siren plug, it is there, but very well concealed. Keep searching and you will find it.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>