Actually, the probe wire looks bad at both ends; as in the insulation is worn off there. But without insulation, I conclude (perhaps incorrectly) that the wire must be at least somewhat continuous because there is only copper to hold it together. Doors have been closed when testing (I hate that dinging :-)

Wore battery down trying to crank it and recharged it again.

Haven't pulled a plug, but I do know that replacing marginal plugs will sometimes get a start where there was none and maybe provide a clue. But I believe I replaced them about 2 years (and 16K miles) ago and would think I would have had poor running on the way to no-start if they were gradually getting fouled. I will try swapping in new plugs.

Thanks for your ideas, as always.