OK, I have a new clue. I checked the wiring harness where it undergoes the most stress and maximum bend when the trunk is opened and closed and did not find any evidence of insulation deteriorization , fraying or broken wires. But I only peeled back about a half inch of the black plastic protective shroud. However, I did have the idea to check the upper stop light and shoot, it wasn't working , nor were the other two stop lights. So I have no brake lights whatsoever, and apparently the two side stop lights are not energized through this particular piece of wiring harness. Since I didn't know stop lights were not working, I did not check if they have a separate fuse. I'm gonna go check that now.
1997 BMW Z3 2.8 Automatic.