The left tail light was normal brightness. The ambient lighting was kind of dim in the storage bay. I haven't had a chance to get into the nuts and bolts yet, but I will before long. Would the tail & clearance lights be split into more than one circuit/fuse? I had assumed that they would be fed by one fuse.
I see two likely wiring possibilities here. One like the white line, and one like the yellow - fed from the left side. That's where my converter is, and where the properly burning lights are. I would think they are run like the white line. When I changed the clearance lights a year or two ago, I don't recall how many wires were at each light, but I'm thinking that the top/right clearance light in the picture was the end of the run. I am suspecting that my problem is in the left tail light assembly connections. That's the first place I'm planning on looking, after the fuses.