Eibenstock ESB/EHB 16/2.1 speed or gear ratio switch. Might also fit similar models.

Required hardware: M4x20mm philips screw, M4 washer (smaller type), 1 spring with outer diameter 6 mm and wire thickness 0,8mm length about 23mm.

I needed to slightly drill out the hole for 6mm, but that's a printer issue. The idea is to let the spring push the slider out, so that it does not switch on its own. Tighten the screw pretty tight, but not very tight