I've looked at the wire connections at the bulb, and even though I didn't actually disconnect them, I did connect my volt meter to them in such a way that it was sampling the wires themselves for power. The wires are definitely going dead - not just a drop in voltage, but an abrupt complete loss of all power. So that is why I am looking upstream for the problem.

I considered the ignition switch also, but the LH headlight and all other running lights continue to illuminate. So, without a schematic in hand, I doubt that there are seperate contacts within the ignition switch for LH and RH headlights.

The fact that the subject head light does work at times tells me it's likely not the fuse. Also, if the problem was a bad connection somewhere, you would think the current would be more likely to jump the bad spot with higher voltage applied (engine running).

One thing I didn't do and maybe should have would be to measure the voltage at the headlight connection with engine running vs engine not running. Not sure what that would have solved but it would have given me something else to scratch my head over.

If I knew where the headlight power wire acually originated from, I could run a jumper to the headlight and see if the problem was in the harness.

The saga continues.....