Woodwhore in that last pic, it looks like the pin is behind the slider for the ball lock. You should put the yoke over the ball, slide the cart forward till the ball hitch is nestled on the U portion. Then slide the yoke back and put the pin through the aligned holes. Not sure if I'm making any sense here or not. It took me nearly forever to get Chazsbetterhalf to lock it as well.
Align the holes on the sliding portion with the holes in the tongue portion and insert pin through the aligned holes.
If it is like the one I saw in Tractor Supply there's two holes, one for using the yoke on a typical lawn tractor with the pin in the forward hole and then the further back hole for on a ball. I recall thinking that might wear kinda quick compared to a ball, but there was no adapter to lose.
Thank you pallet pete, the whole setup is only a few months old and iv moved alot of wood already, so nice not using the wheel barrow anymore.
I have the pin in the rt spot, i havnt had the trailer and quad together since that day. Today ill see what i can do.