Thank's Dave, you are generous to help with my "can't see the forest for the trees" query. I think of your kindness every time I order from Pelican.
What tripped me up was the hot terminals had continuity to ground even with the ground wire removed. Obviously, the entire fixture is grounded to the chassis as well.
As you surmised, I'd plugged-in the harness incorrectly. The diagram I'd drawn was turned 90 degrees. Working late is dangerous.
With the terminals correctly connected everything works fine. At last, I have parking and side marker light on the driver side. I also made a new diagram for next time....