There's a very simple, but hard and fast rule about backing up that I haven't seen in any of these lessons. This rule works 199% and has been invaluable to me... (When I remember it...)
Most pilots get confused very quickly, when backing, mostly because of orientation and the reverse view in the mirrors...
So here it is...
When backing up a normal rig (5th wheel, or TT...) the first thing to do is drop your hand from the top of the steering wheel to hold the bottom of the steering wheel... Now when you "push" the wheel, the back of your rig will move in that direction! If you push the steering wheel to the right (from the bottom) the back of your rig will turn to the right.
Another way to wrap your head around it is...
The direction of the BACK OF THE FRONT WHEELS on your two vehicle pointing is where your rig is going to go.
In other words, you've turned you steering wheel all the way over, like you are going to make a hard right hand turn (moving forward) the back of your front tires is pointing to the left...
When you put your tow vehicle in reverse... the back of your rig is going to go to the left.