Blower Wiring?

I just picked up a "surplus" small squirrel cage combustion blower, it has 3 wires coming out of the transformer,
AND a separate wire for ground to one of the screws.

I matched 1 up on each opposite sides and plugged in and the motor works, there is another wire coming out of the same side but bottom of the transformer, not sure if it's a dual speed or a secondary tap to change the speed? I don't know what will happen if I hook it up instead, slower/faster? short circuit?

Thanks