On the interior light switch, i think it's a thing in older vauxhalls. But I never new that when I had my second car, a '96 astra f. For NINE months, any time time I needed interior light (Pulled up eating pizza with a mate and the like) I would open the door. Only when my friend was driving the car one night with me in pass seat was "it" discovered. (He drove a Volkswagen) there we were, 11 o clock at night, poor weather, just driving along when suddenly the interior light came on. I thought something had faulted and said nothing until my friend said, And I quote ...."Well... I was actually hoping for fog lights but I suppose this'll do."... Commence dangerous laughter fit at my pillockery!