Thanks for the quick, expert replies. I now have headlights! 

The problem was, of course, the grounds. My install of the relay
upgrade two years ago apparently separated the wrong ground wires
(there are a few pairs like that behind the fuse box) so the headlight
grounds were still stock, stuck together on one connector, corroded,
and a bit burn looking - probably from that night I drove home a
couple of hours without low beams and some masking tape applied in
stripes across the hi beams to tone them down for oncoming traffic.

My headlight grounds were attached to the ground cluster closest to
the front of the van behind the fuse box (reach back further and
gently pull aside the mess of wires there to make a space to inspect
and clean these connections). Once the ground spades were cleaned up,
the two wires separated with new female spade connectors, and
reattached, the lights worked perfectly. I thought about the good
suggestion to ground the headlights closer to the lights themselves,
but I decided to leave that for another time.

Thanks again. I found Kim's detailed discussion of troubleshooting
very helpful; Dennis knew all along it was the grounds.

Off to Big Sur (Pfeiffer Burns SP) this Sunday/Monday ... wouldn't
have gone without the headlights working....

PG