You can find quite a few threads covering modern Mercedes, BMW and other German makes that have one-side-at-a-time parking lights as a standard option. But I can say that this is not a modern option at all, and while I don't think it was ever common on American cars - big,wide streets and all - it was certainly a feature in '60s and '70s German cars. Perhaps this was an option available for Morgans sent to Germany? Pre-wired/dealer installed? Just a guess. Saw interesting photos on Google of new MB's with two switches to select either left-side or right-side parking lamps.
