Well, I'm all lit up again and the alternating brake/amber turn signal flashing is gone too.
Don't know for certain what all provided the "fix", but what I did was replace several bulbs of obvious cheap sourcing (unreadable numbers printed onto the bulb bases instead of stamped in like quality bulbs) with the better quality, replace a dead license plate bulb and clean up all the harness grounds. There are three grounding sites in the trunk, one on each side of the inner sheetmetal structure behind the wheelwells and one beside the driver side tail light housing. Two of the three ground sites had obvious corrosion once their fasteners were loosened. You couldn't see that with the nut/bolts in place. A little emory cloth, some electrical contact cleaner and a coating of dielectric grease and everything's working well again.
Thanks for all the suggestions.