You know... now that I think of it.. this should be VERY EASY to resolve.
First pull out the alarm horn and put 12 volts to it. That should tell you if the horn works.
The horn has 2 wires... one is brown (ground) and the other is Black w/yellow stripe and red dots. This black wire is wired directly to one of the alarm plugs (ok... maybe it makes a stop at the fusebox... I don't know.. will have to check alldata). Just unplug the correct plug and test for continuity. Also test for continuity between the brown wire and any ground on the vehicle.
I just installed a bergwerks keyless entry system in my car. Currently the lights flash when opening and closing. I just purchased another relay in order connect the alarm horn as well.