The plug has 3 wires, black red & blue.
I'm gonna take a guess here, (that it's similar to the electric I had on my old style Bronco).
Black should be your ground.
The Red should be the high speed hot wire.
The blue should be the low speed hot wire.
You should be able to bump the wires to a power source for a second to confirm this, (without any damage to the fan). Or if you have an ohm meter you could check the resistance between black and red/then check the resistance between black and blue.
If your ohm reading is a higher resistance on the black to red / than the ohm reading on the black to blue / that will confirm high speed.

Jeff
http://www.fordification.com/forum/view ... 22&t=46251
SOLD-71 F-350 dually flatbed, 302 / .030 over V-8 with a "baby"C-6, B & M truckshifter, Dana70/4.11 ratio, intermittent wipers, tilt steering, full LED lighting on the flat bed, and no stereo yet (this way I can hear the rattles to diagnose)! SOLD!
Many Ford bumps / one 76' EB / and several dents through the years.
A lot of "oddball" Ford parts collected from working on them for 34 years now!
2008 Ford Escape 4 x 4