the dark box below the table attack to the back brace, with the rod going to the pedal. is the e controler aka foot pedal, you can also see the knee lift
singers #404 cabinet kinda hides all that. I've tired to look up the singer 404 cabinet all I get is a u tube vid that I can't load. if you look in at singer 15-91 manual on about the 3rd / 4th page it shows the 404 cabinet.