I did the relay mod and it seemed to stabilize my charge at 14.5 volts while cruising, but I did notice at idle in gear about 750 rpm my volt meter is bouncing between 14 and just under 16 volts.
That's odd that your voltage would be fluctuating to 16 volts at idle, do you have a good ground on the regulator? 14.5 is what I set my adjustable regulator to at cruise. I am at about 13.6 volts at a 800 RPM idle.