I don’t have the hitch option (receiver adapter and wiring), but I’m ordering the bits to get my tow game correct. Above the hitch, on either side of the big black hook ring, there are holes in the bumper steel. The left hole houses the trailer wiring plug sockets. What is the right cutout for? If it’s unused, is there a blank for it—it’s kinda ugly?

What goes in the second hole?!

 

Here you go

 

Looks like the British electrics use both holes
My OEM US setup only fills the left hole - never bothered me

I'm sure you could find a generic rubber body plug (solid grommet) that fits well enough