Does the light work? When key is turned on the light should be on before the bike is started.
Maybe the RS is idling to high? The light goes out on a lot of the Airheads at only 1300 rpm. Does on my R90/6 and many others. Will almost always go out by 1500 rpm at the highest.
The ultimate test would be to check sitting voltage of the battery and charging voltage of the system when idling and when the rpm is raised.