Bob,
Thankfully it happened afterwards - in your driveway! From a remote arm chair, I've studied the early wiring diagram and see that the light switch (circuit breaker) is "down stream" of the ignition switch. If I were under the dash, I'd be concentrating on the ignition switch, ammeter, starter (you've already been looking at it) as well as the starter switch and even the voltage regulator and coil. -They're all connected in front of the circuit breaker.
My limited personal experience with the circuit breaker is it works when there's a short. While a loose connection could keep a component from working, I don't believe that alone would cause the cb to trip (no circuit vs. overload/shorting).
I think back to when I was troubleshooting electrical systems and we had the luxury of isolating amps and volts - much better than volts alone. One of the initial checks was solenoid symptoms when attempting a crank. A chattering noise usually indicated a weak battery. A single solid click usually meant starter/solenoid issues. USUALLY....
Could the breaker be bad? Maybe, but it's after the ignition circuit and since it's tripping and resetting, I could incorrectly assume it's working. I'd be looking before that.