Thanks Pcomm,

I came across that article in my search, but the walkaround is new to me.

Even though it's an odd location and angle, it has to be a brake light, the others must be running lights since there are four. It has a thin lid held on with screws and what looks like a lens (other pics I found it was broken). It's tack welded, so it wouldn't be a support for something, what else would it be?