Older Janome machines have a flat rectangular motor connector with three or four flat pins.
The connector box is the same for both, but the 3-pin version simply lacks one of the pins.
The lacking pin is earth – second from right on the motor socket. It is only required for motors and pedals with a metal body, or if you also needed to earth the lamp. Newer plastic bodies are already insulating the bits inside, so there is no danger of electrocution.
Here is how such a connector is wired, this is the top part:
Here we have a plastic-bodied pedal and a 3-pin connector with an empty position for the earth wire. Brown is live, blue is neutral.
Janome also had similarly looking connectors with round pins. I’ve never had one of those personally, so don’t know how they are wired, and it could be different! Best verify to be sure.