Wiring direct to battery?

[Jules-C]

Ground the neural side of the equipment down to any convenient point on the Frame (The whole of the Bikes metal structure is the Neutral side of the circuit) or handlebars, as long as they are not rubber mounted for vibration absorption.

I wouldn't recommend handlebars since you've got to get a connection to the frame through the head bearings and there should be grease in there keeping the metal parts from touching.  Probably work for most things but better going back to frame