what is happening when you turn/try to turn the nuts is the shaft turning are they not moving..2 nuts.. is there one screwed down to a second one on the threaded shaft
that is correct
and as stated
the black/yellow and black/green must be tail light right and left
and they must both go to the one beside the white..which should the brown wire on the other plug
the black/yellow and black/green must be tail light right and left
and they must both go to the one beside the white...never seen that but can't be anything else..... imho
I don't know the unit but most times they just plug into the vehicles wiring harness , so one set of wires should be going into the box and the other wires should be going to the trailer and if the is the case it is pouched