@CzechPassat, good work, well done. 

@J.R. the circuit diagram that includes this Hall effect sensor on the clutch master cylinder shows it like this, which I think is meant to show a 'virtual' normally closed switch controlled indirectly by the hall sensor and associated electronics. There's also a normally open switch not used in this application.

Rectangular box with 26 inside is a fused 12V feed, connection other side of NC switch is to engine ECU.

 

Success!

 

I reinstalled the old switch on the new master cylinder and everything works as it's supposed to. Looks like the new master cylinder came with a faulty switch.

 

Many thanks to Breezy Pete for providing the information I couldn't find elsewhere.