Thanks very much again, Bernie.
My car was French-restored and, without wanting to sound Francophobe, I’ve already noticed a couple of other unusual Gallic approaches to the wiring installation.
I’ve found the French instructions for fitting the sender amongst the car’s paperwork and the in situ wiring doesn’t look like the diagram provided, so I’m going to correct that.
I think it won’t do any harm to fit a heavy duty 12V/6V converter and run the clock and the presently unconnected wiper motor through it because there’s nothing to suggested that their voltage has been modified.