Single phase motor I take it? There should be a wiring diagram on it somewhere. Maybe under the cover for the wiring connections. On a 1 phase motor the low voltage diagram would be for 110v and the high for 220v. It shows which wires to connect together. L1 and L2 are the wires from your power cord. To put in a switch take your power cord and connect the black to on leg of the switch and then continue a black from the other leg of the sw to the motor. The white does not need to be connected to the sw. it just goes around it as does the green ground wire. You need to go from the center "round" plug all the way to the motor and connect to a green screw or the chassis of the motor. If you are not sure or confident I suggest a trip with motor and switch and plug.to a electrical shop. Probably a how to diagram on the web or get a electrical book for dummies at the book store. Fires and shocks are not good.