I went with this setup from
http://www.hollisterroad.com/ for my 95 Taurus 2 speed fan.
Just throwing another option out.
I purchased the kit with the 180 and 195 sensors.
Was very simple to install. The wires are very heavy gauge (10 Gauge off the 3 heavy duty relays)
I ordered a Painless 3 wire connector at the fan plug in to make it weather proof and easily maintainable.
On my setup the low speed fan comes on at 180 (20 amp draw) if needed it then steps up to high speed at 195 but with a low start draw because the fan is already spinning. (low speed shuts off) Typically would be in the 40 to 50 amp range depending on the age of your fan motor.
When it drops to 180 then the high speed shuts off and low starts etc..
I received a bad 180 sensor when I purchased the kit. It was easily bypassed until I could determine what was happening. I emailed him that I didn't think it was working as described and left my cell phone number. He called me the next day (and also gave me his number) and had me do a simple ground test with the fan to verify that the motor was indeed working correctly. He said it was a bad sensor and he overnighted me a new one. (great support
I went with this setup because they got great reviews and I'm not a wiring expert. I probably could have made one similar/cheaper after seeing it but the amount of time I would have spent figuring it out would have out weighed the cost. (in my opinion)
FYI, This setup will work with LS series motors and PCM's
Couple of pics of setup.