security system does not chirp after horn replacement

hi,
my stock 3-terminal horn died, so i bought a new one. new horn is a
regular one and has 2-terminals. i figured out which of 3 terminals in
horn connector are +12, and horn control button, and wired them to the
new horn.
the horn sounds fine, but security system does not chirp anymore when
armed.
does the 3rd terminal in horn connector have anything to do with
security system?
i assume that the apendix attached to my old horn was a relay. do i
need to take any precautions when wiring a 2-terminal horn? do i need
to make use of the 3rd terminal to enable security chirp? how do i do
that?
thanks all.

 

Is this a Saturn you're talking about? I cant tell.

 

it's Saturn SC-2 '99.
thank you.

 

From what I've seen your theory is correct. The 3rd wire appears to be
another ground which is completed by the alarm system. Basically you
have no alarm sound now because it has no way of grounding the horn. Now
the question is can you tie the 2 ground wires together??? I am not
sure, it could cause a problem or it may work just fine.

 

the strangest thing is that when i connect a siren from my home alarm
instead of horn, the siren works both as a horn, and as security chirp
(even withought the 3rd terminal connected). however, when i replace
the siren with the horn, there is no chirp.
the siren has a polarity, and i thought maybe the polarity makes the
difference. so i placed a diode in series with the horn - still no
chirp.