Voltage monitor on a Firebolt

[MustangGuy]

Has anyone installed a voltage monitor on their Firebolt (or any other Buell)? My 03 'bolt has charging issues - I think I've isolated it to the original regulator connector (77) but that's a different topic - and I picked up a neat little monitor from American Sport Bike. It's supposed to be easy to connect: red wire to a switched source and black to a ground but rather than making a slightly educated guess on what wire to pick for the switched source I was hoping someone else might have some golden advice!