Strange LED back light issue

Just to know, I’d plug it into the truck and see if the whole thing still ever lights up.
Most LED truck light failures I’ve had (which is a bunch) involve several of the individual segments failing, sometimes only a few still working.
Then after I knew that I’d start troubleshooting more and see why there’s any power at the tail light at all when not connected to the truck. It only takes a tiny amount of current to light them, I suppose it’s possible there’s a certain point where just those segments will start to light before the rest do.

Maybe something crazy like the truck connector cord is full of water and just enough current is getting across the terminals from +12 to that tail light’s terminal.
Try blasting the connector with WD40.

CAN WE ASSUME that this is the original factory wiring ? not a DIY conversion?
bumpy

Could be a poor ground (even inside the light) or RF or just noise on the power from something nearby. Is there anything else that's on in the RV?
If so I would try turning everything else off and even unplug the rig from power.