. I can't recall any shift switch on my Yanmar 6LY with a ZF 220 transmission. So I think it is part of the throttle/shift lever mechanism.
I got the ZF tranny and pretty sure there is a switch down there, if not, then on the fuel control unit: Canít start out of idle, or out of neutral.
I replaced the dual throttle/shifter with the 2 levers a year ago with a single lever
Teleflex/Morse unit. No electric wires going up there but instructions and connectors for hooking it up, figured I was not protected..Wrong.
Turns out there is a Yanmar or ZF switch somewhere down in the engine room providing the same protection.
Did not have a chance to look today, but will do tomorrow.