Hi Robb,

Intermittents are the most challenging of all troubles, and ideas like rigging the timing light are those of a patient and thoughtful troubleshooter. Whether you employ that specific method depends on how frequent the trouble recurs and how long you might suffer the kludge of the trap waiting for it. To me, it sounds like a good idea if you're the only driver.

I once went with an annoying light added to the tach, pulsing with each spark, but that only verified the ignition primary, where your idea would verify spark after the coil. It was Mrs. B's car, so I couldn't ask her to ride around with a timing light laying on the seat.

Would the ig switch be more like to interrupt spark or fuel if it was bad?

The ignition switch has three sections providing power in KP-II. Only one of the three is needed for engine operation, and that's the one that also provides power in KP-III, the cranking function. That one supplies power needed for both fuel and spark circuits, and, interestingly, turn signals. So, if you suspect that part of the switch is open at any given time, suddenly inoperative directional signals (not hazards) would confirm your suspicion.
--
Art Benstein near Baltimore

I totally take back all those times I didn't want to nap when I was younger.