The two horns under the hood do work together at the same time to produce the "dual-tone" that you hear when the horn honks. If you disconnect one at a time and honk the horn, you will hear the difference.

I'm not sure if your 99' factory alarm works in the same manor as my 03', but their is a way to add a "beep" if it does. I've already addressed this in another post. Do you press the lock button once to arm/lock the doors then press it again to get the horn honk? If so, then it's the same as mine. I have added a beep to my factory alarm very easily for less than $20. If you are interested, check out the other thread for more details.

https://www.honda-acura.net/forums/s...d.php?t=277753