Brian,
The first set I bought ... one went on the backrest, which it is made for, with no problem. But, that sharp edged piece of metal chipped the saddlebag lid the first time I closed the bag

The locks are made for the "outside" of the detachable's. You are trying to put it on the inside for the tourpak. It did work, and you need to either bend the key of cut it. I did both, the short key I threaded a acorn nut to the cut end and leave it under the gas cap door.
I had to fiddle a bit to make it work on the tourpak.
I bought another set because I also have a back rest for when the comfort stitch seat is on, and a king tourpak. I can not get the lock work on the king pak!
I don't know why they can't just make a lock for tourpaks.
During our recent trip I was running a cable lock through the tourpak every night, what a pain.
I am now thinking of drilling a hole and running a bolt with a nylok nut through. Will keep the quick grab it an run thief at bay and the lock won't stop the better thieves anyway.