Seat belt laws?

I got pulled over once for "not wearing a seatbelt" and explained I was wearing my lap belt. When the officer asked about the shoulder belt snapped on the roof I told him it was an option I added, but since it "didn't have the correct bolt" it was there for decoration only, and wouldn't be safe to use. He just nodded and said "uh, OK Iguess" :)

Grant