Hey Empluserider,
I can' find the post but someone asked Brammo what the voltage was in our stock system and according to the Rizoma instructions, you should use one. Someone also mentioned that while one might work, the more LEDs you add might not and you might get a faster "blink".
Anyways, I ended up hooking them up to each light though didn't test if it would work with just one on each circuit.