Greg,
Tim speaks the truth on all points. If you want a third wire for ground that's perfectly fine. Many of today's housings are plastic which requires this ground wire anyway. If you choose to run a third wire to ground the housing (or any other electrical item) the connection points must be clean and well attached...just like the housing/bracket should be. It's sort of like "six of one, half a dozen on the other" as I see it.
Many folks don't stop to think that even though you don't see it, the ground path is really a 'wire' that completes the circuit to ground..it just takes the form of a bracket or a frame rail or a fender etc.
Stuart
