But, but, but... you're going to want a switched 12V power source soon anyway. How are you going to power the heated grips, seat, vest, and all the other farkles? I mean, if you don't have all the farkles, you wouldn't really need the Datel, right?
BTW - I considered the mirror install, but decided in favor of the right side panel ("D" I think) next to my 12V powerlet connector and just to the rear of the battery itself. That also made wiring shorter (a plus) and easier. I put my 12V 30A SPST relay (readily available at auto supply houses and even Radio Shack) in the front faring and secured it to the subframe ahead of the battery. The relay has heavy wires going back to the battery + terminal and separate heavy wires feeding the heated grips, heated seat and Datel. If I add one more farkle I will rewire to include a Blue Sea distribution / fuse panel that I already have sitting on a shelf, but I can't seem to find an ideal place up front for mounting.
Anyway, the point is; Try to keep the runs of large gage wire and as short as possible.