You could just hook it to a switch. I'd go with a thermostat and relay though to be on the safe side. you could wire in an over ride switch and maybe an LED to remind you you in over ride mod.
Found a schematic for a 2 speed fan, which I believe some of the Taurus fans are.
Make sure it is wired so that only one fan is on at a time , otherwise the life of fan will be shortened ,, use 2 relays ,, Ford used a 75 amp , but 30, 40 and 50 amp have also been used pics courtesy of the web
The 2 relays are Ford Taurus OEM fan relays. The 87A contacts are normally closed. When the van's ignition is switched on, relay #1 is energized and sends power to the 87 contact and on to relay #2. Relay #2 then sends that power to the 87A contact and on to the fan low speed. When the thermostatic switch is activated it will switch the second relay to the 87 contact activating the fan high speed.
To wire the manual on/off switch, add a wire in between the van's switched power wire and the #1 relay. . The LED is wired to the normally closed 87A contact on the #1 relay. Use the relay to cut power to the LED when the van is off, otherwise it will blink when the van is off.
