The potentiometer method is fine for controlling the instrumentation used ie it varies the voltage to the easily replaced lamps used in the instruments.
The implementation is the problem.
Probably the value used could do with investigating so that there is more fine control and certainly in the OP's case and probably others the mechanical instalation should be solid
Should I go to the extreme of installing a variable DC:DC converter?
Is it simply that they don't expect people to drive the cars in the dark and wet and that they mostly end up as garage ornaments that these areas get overlooked? Playing on the fuzzy feeling that owning a Morgan is supposed to engender that we will happily overlook things that simply would not be acceptable on other marque of cars?
They maybe based on traditional values and designs etc but this is the age of information and potential owners will be able to easily find out about any shortcomings much easier than any time in the past. Quirks are one thing that people will put up with even find them as part of the character but FAULTS overlooked by the factory are likely to have a detrimental effect on possible sales.
Silly little things like this should not happen.
