I checked the trailer connector with a multimeter and the running lights blade registered voltage fine. No corrosion on both sides either.
I did notice that the each front side marker light is on the same fuse as the rear running light. The fuse is good and the side marker light is working.
I tried tracing the wire back, but on the ground there is not much room to work, so I don't see anything as far as I can trace it.
It looks like the passenger rear light assembly wiring harness runs across the frame and into another harness connector near the driver side rear axle. There seems to be a handful of connections feeding into this point. No visible damage there either.