On the number and shape of my swamp cooler motor cord terminals
That looks like an Adobe P2-911 plug and it is proprietary. There's another version Adobe made (I believe it's for the 230v motors) that has a 5th round pin. The flat bladed terminal is for keying the connector so it can't be plugged in upside down. You should have a 115v cord with 2 hots - one for high speed and one for low speed, 1 neutral, and 1 ground.