I recently installed and recorded detailed instructions on how I added a Screaming Banshee Full-Split Screamer horn on my MP3 250. The same process applies to a 400.

To disassemble and reassemble the windshield and front end of the MP3, please watch Mic Bergsma Productions fantastic YouTube video tutorials before you watch mine. They are the 3rd and 4th video below.

FYI. The video begins with an image that illustrates where I installed the horn and routed the tubing.

Details about how I successfully installed the horn

How to remove the windshield

How to remove the front end and headlights