Finally got around to this. Pretty simple, about an hour, start to finish. I only have the one picture, showing where I mounted the horn. The M225e (and probably the XG3025) have an unused bracket on the front of the firewall, on the ignition switch side. Probably for a horn on a more deluxe model. Was able to put a 90 degree bend on the straight bracket of the motorcycle horn I bought on ebay. Tapped into the positive lead I had put in for my rear light, and there was a very convenient grounding nut just a few inches below the bracket. Simple, momentary rocker switch is also from ebay, has the horn symbol and "Horn" on it.
Here's the under the hood install:

Here's the under the hood install:
