My brother had one as his everyday car when he was stationed in Germany. Don't think he used a light switch for ignition, though.Hadn't thought about it in years.
In the '70's my dad had a '58 DKW as his hobby car. He had the ignition out for some reason and replaced it with a light switch. oYu turned on the switch, touched the loose wire to one of the contacts and the car started. I'm driving it one day, out with my friends and we get pulled over to a roadside random safety test. The tester was confused to say the least and I was so flustered that when it was time to leave the testing area I forgot to turn the switch and it wouldn't start. Finally calmed down enough to remember. The car itself got a warning because one of the headlights was aimed improperly. My father grabbed a screwdriver, drove back to the testing location, popped off the trim ring and adjusted the headlight. easy peasy. Needless to say the testers had never ever seen a DKW before.