And the answer is......

TWO low beam filaments burned out at once!  I pulled each headlamp element
and checked their continuity with a voltmeter.  When the first one showed
one filament as broken, I thought Uh Oh.  Both elements were burned, I
replaced them, all is well.

This solution is too easy, but highlights an important lesson:  Don't make
up your mind that the problem is serious until all the FACTS are in.  I was
unwilling to consider that both elements would be toasted at once (what are
the odds?) and so casued myself much anguish.

Many thanks to all the list members who chimed in to cause me to slow down
and look over all aspects carefully.

Mark Williamson
Denver, CO
88 Wolfsburg Weekender