In almost all cases the original twist lock on the outside of that metal door (called the Cage door) that covers the secure USB ports on the left side on the front of the brainbox is gone. That twist lock just had a cam behind it that simply rotated behind it to close a roller switch that's behind the metal door on the brainbox itself.
The actual switch behind the metal door is basically just an L shaped piece of metal. When the two wires that go to that switch are connected to each other, it's closed, when they aren't, it indicates open.
To get it to indicate closed. Just fold up a post-it note or a small piece of paper and wedge it inside the gap of the L shaped metal part sticking out. That presses down the switch, you can see the roller switch in there if you look closely. You know you have it closed when the "C" is no longer highlighted on the switch status list displayed on the upper right of the main screen. Then anytime you need to modify anything with the ekey, you just have to remember to remove that piece of paper or it won't allow you do do anything with the ekey.

If you take the lid of the brainbox off, you'll see the two wires going to that switch. There's no other wires around that area.
Personally, I make it easier by removing the two wires and connecting a simple SPST toggle switch and connect each wire to it. Then that toggle switch connects and disconnects those two wires from each other which results in the "C" indicator going on and off.
And I use extra wire so I can run the switch to the top main door area so I can open/close that switch without having to open the lower door. And also have USB extension cables to the secure USB ports. So to do anything with the ekey, or do anything. I never have to open the lower door again since I can plug in USB keys and open/close the "C" switch from the top door as well. Doesn't take long, and removing the lower door is a pain in most cases. Then I can do everything by just opening the main top door, flip the toggle switch, and have the two secure USB port extension cables to plug into behind the top main door. You cannot use a USB hub. Only individual USB extension cables, one to each port on the brainbox. And I just leave the metal door open. Or even cut it off so it isn't in the way. lol