Follow up to my previous post - I carefully scraped the insulation off one side of the wire shown above and soldered a wire to it. I then put a connector on the other end and hooked it up to a press switch. I double checked the voltage across the switch with the ignition on and it showed the expected 5V. I then followed the programming sequence in the Morgan Three Wheeler Club note and everything worked as expected. One note I would add is that a 'long press' means hold it down until the display changes as expected.
My M3W was shipped from the factory with the pulse setting at 3295 (not 3795 that apparently is normal), which explains why the speedo was over-reading by about 20%! Next long trip I'll double check the Avon setting of 4060 against Waze.
Others who can't find the programming plug may want to see if they can spot the black/gray wire to avoid having to remove the bulkhead, although you do have to risk cutting the wire when you strip the insulation so you might prefer Lance's approach if that scares you.
