Diameter is 3.25"
My needs are either driving lights or fog lights...can't really decide, its foggy in the winter mornings in West Sac, CA but that's about it.
I checked and the wiring is already set, just need the switch and the lights. Interestingly enough, I found this kit:
I emailed to see what is needed for application, but I'm guessing they won't know/care. I might pull the cover off this weekend and see if there are any mounting holes/brackets built into the stock covers.