The controller was installed under the bottom drawer and this is what it looked like when it was in place:
There's a notch carved into the side wall of the cabinet and there's an arm which sticks out of the notch. Keep in mind, you're looking at this with the cabinet turned upside down. The arm is where your right foot would be if you were seated at the machine.
Here's a closer view which shows you the part number on the controller:
Viewed from the top (after I removed it from the cabinet), you can see how this worked. There's a little rounded nub on the end of the arm (it's at the lower edge of the next two photos) and that's what you would have pressed to engage the controller. Pressing down on the arm also allowed you to slide the entire arm into and out of the cabinet so it would retract when you wanted it out of the way. The top photo shows the arm extended and the second one shows it retracted.
I kept the controller because one of these days, repairing it might float to the top of my "to do" list. If anyone knows where the wiring should run in the cabinet, please let me know. It was wadded up next to the controller when I bought the machine so I'm not sure what route it ought to take to get from the controller to the machine head.
Happy Sewing Everyone!