Always thought the single AC Delco low tone (405 Hz) horn was insufficient. Didn't help that the car was so small, and black. Finally got around to adding a louder horn. I've had air horns before, but was disappointed. Mostly because they were even higher in pitch than stock, so it didn't have the low "truck" like resonant tone. Finally found a nice loud one with a low tone.
Forgot to add, since the compressor in the air horn takes a brief moment longer to spin up than the OE diaphragm horn, when the horn honks with the keyless, it's only the OE horn you hear, the compressor just really spurts to life briefly without really making a noise. So you really only hear the air horn when you press the panic button or use the horn on the steering wheel, and not with the keyless. I've run into this before, and it's part of the reason why I like adding air horns, instead of louder diaphragm horns like Hella Supertones. Again, just my personal preference.
First 2 beeps, stock horn, 2nd 2 beeps, both borns. The Wolo 619 plays a 320 Hz tone.
DSCN3269I used a typical 4 terminal automotive 12V 30A relay. I use the stock horn wiring to trigger the relay. The air horn gets it's own dedicated power line instead of tapping power from the existing horn wiring.
Parts List
1) Ring terminal: To get 12V power
2) In-line Fuse holder: <img>
http://i.imgur.com/XDFMfpy.jpg</img>
3) The horn installation instructions suggest a 20A fuse.
4) 14 and 16 gauge automotive grade wiring: will depend on where you want to mount your air horn. I mounted mine on the driver side below and behind the headlights, past the end of the metal bumper. The recommended minimum was 16 gauge for the power line. I used 16 gauge for the trigger line, which had a recommended 18 gauge minimum. Just my preference when doing electrical.
5) 12V Automotive Relay: I suggest using a minimum 30A relay since the fuse is a 20A fuse.
Female spade terminals: <img>
http://i01.i.aliimg.com/wsphoto/v0/361731849/Brand-New-Red-22-16AWG-Insulated-Female-Spade-Terminal-Connectors-Wholesale-EP144-.jpg</img>
You'll need them for all the connections to the horn and the relay.
6) Air horn: I used the Wolo 619 due to its low frequency.