Off the pot. Onto the compass.

Instead of a synthetic potentiometer input, we now have engine light-up (well, LED light-up) running with real live compasses.  Jubilation prevails.

Only downside - the code has to be fine tuned for each individual circuit, which has to be fine-tuned for each individual compass.  But, four unique bin levels isn't all that bad.

I just hope the boat's vibranium coating will cut down on signal noise like we expect.