[Werner]

Thank you very much for the help so far!

Joe, it's the 3-contact switch. The car used to be converted to a double light bulb (no difference to be seen). No housing markings to be seen.

Eric: Yes, I read this information. If I understand it correctly, is the plate not too thick, but its circumference too big? In any case, the case is very tight.

Wick: The switch spindle has only 1 groove for the horseshoe clip at the bottom. I have the tool to compress the spring. That is tight. But when I switch the lights to the right and left, I don't feel that they really click into place. The steering wheel lever turns tenaciously and unevenly, but no noticeable clicks felt.