BTw - the one I showed has a pig tail hanging down from the underside that the foot pedal plugs into. I've got others in cases that have a female end in along side the male end under the motor, and the foot pedal has a longer cord that plugs into along side the power cord. that is why there are two round areas, but only one is cut open for this machine.
I'm pretty sure Chicago plug refers to this type of connection. I have several older Singer machines that use this style, and they are much older than the National machines I have using the two round prong connection. My older Nationals are wired differently.
