I just put in the Wolo 320-2T horn mentioned by turbo2ltr on page 2. Quick and easy, glad I read through this topic to find out about the release button on the connectors. My positive terminal release button was mounted towards the old horn, so I needed a small screw driver to push it down while pulling it off, not so easy in the tight space.
Attached the ground wires provided to the brackets, made a pigtail using the male connector from the old horn, and did the vertical mount using the original bracket as attachment point. Left the original ground connector unused to blow in the wind. Had to find a bolt that fit the hole on the original bracket, as the supplied bolts were too thick. Worked fine, nice and loud.
They are available at any local store, but here's the amazon link:http://www.amazon.com/Wolo-Model-320-2T ... 999&sr=1-1
You can hear a sample here, down towards the bottom of the page:http://www.wolo-mfg.com/elec.htm
There are also several videos available on the web of different horn sounds.