Well, I found the offending ground, and it was the right front turn signal. I had only looked inside the housing and at the pigtail, ASSuming that the ground wire was directly at the socket, not on the outside of the casting.
I had a minor fender=bender last year, and it appears the body shop lost the correct screw for the ground and used a long sheet metal screw instead... so long, that the wire was loose. Worse, it was a much larger diameter that needed and split the lug on the housing.
For the short term, I found a shorter, similar thread screw and have things operational until I figure out a way to properly repair the lug or create a different ground. I'm thinking of trying a dab of Frost King defroster repair epoxy which is conductive, to repair the lug.