Last night I did some checking. The wire had continuity to ground, zero resistance. With it not connected, voltage across the battery terminals while running bounced wildly showing 12v, 0v, 30v... skipping constantly. When I attached the mystery wire to a good ground point on the frame, voltage across the terminals stabilized varying only from 12V to 15V, and never showing less than 12v. It seems to me to be a charging system related wire, but weird that it goes into the harness heading towards the front of bike, when my regulator and rectifier are under the seat. Is there a ground for the ammeter that must be hooked up for proper charging, or is that grounded simply from being mounted to the metal nacelle?