I´m running dual electric fans with a thermoswitch from Ron Francis Wireworks wich sits in the intake next to the thermostat!It works great and between 161° and 176°,The temperature is about 15° higher in the intake so the switch with the lower temps is good.
Otherwise it should be mounted in the head where the sensor for the tempgauge sits!
Look here :
http://wire-works.com/accessories.php
Its the AR-33!