We should probably move this to the Rider section soon (if this disappears, that's where I've put it), but ...
I don't know what the Ultra has for audio input as config'd from the factory, but here's what you're looking for from your Rider2:
Pin 1 = Orange = Ground (too strange)
Pin 3 = Brown = Line Out
You'll need to find a line-in / aux-in somewhere on your Harley to send that signal to.