I bought an electric fan but have not installed it yet. I struggled with the same temp switch issues. Then I discovered a switch that simplifies things a lot. The switch is sold by Speedway. It is adjustable too. It requires that you have an electric style temp gauge. The temp gauge SENSOR sends a signal to the temp gauge just like usual. I plugged mine into the water outlet that connects to the upper radiator hose. So the electric temp gauge is setup just like you normally would.
This fan control switch (sold by Speedway) taps into the gauge wiring and you can tell it when to turn on by using the actual gauge temperature.
Even though I have not wired mine up, my friend has the same switch and is happy with it.