If bypassing the control box works, you'll want to use a relay.
Bosch relay number 0 332 002 150 (Echlin AR298) is a 75 amp relay.



Note the measurements are metric.

You can run this in conjunction with a thermostatic switch to control the fan.

If wiring the fan directly works like my shop foreman stated, you should be able to use high and low speeds. One switch for high, one for low.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon