Unplug the fan motor compeletely, and run jumper wires from the battery in the car, the cigarette lighter, or from another battery. You just need to put 12 volts across the motor contacts briefly to test it. I rigged up a cigarette lighter plug from Radio Shack with about 12 ft of speaker wire so I could take it all around the car to get 12 volts to things for testing.

The power is always hot to the fan motor even with the key off (be careful when you work around it), so for this, I guess you just need to ground the ground side to the chassis. Jump a wire from the ground connector to a decent ground point, bypassing the regulator.

Brett