Before getting all carried away reinventing the wheel, why not just forget the Harley system and wire a regular remote from your garage door opener to a simple momentary switch, then mount the remote inside the fairing and the pushbutton switch where ever you want it? That's how I have mine set up now, since the Harley system wouldn't work with my new whiz bang opener from Chamberlain. It works much, much better now, with range of several hundred feet versus barely 40-50 feet with the Harley system, and it works first time every time which I can't say about the Harley system.
I understand the desire to figure it out and make it work, since my mind is wired that way also, but there comes a time when it's better to just go a different direction.
Jerry