Finally Installed my Train horns.
I have the S4 kit from horn blasters. Its pretty loud.
Video:
http://www.youtube.com/watch?v=4jgsPFx1Mzo
There Louder in person, i taped it on my digital camera.
Also, You cant see the Horns when your looking at the truck, you can only see them when you pop the hood. Or if you have a flash light.