You should run relays on a fan....
Here's a circuit that you can put in that will do some nice things...
It turns the fan on automatically at the temp the sender is set at.
It turns the fan on as soon as the a/c gets turned on.
It gets turned on manually with a switch (cruise parades, etc)
You can't forget this one, and it won't pop fuses or breakers.
Uses standard automotive relays.
I set my truck up this way and it works great.
http://community.webshots.com/album/79580450MvBZqX
Jeff