Adding a manual fan switch to your SVO - by Chris Roth
The stock engine fan controller does not turn the fan on until around 226°F.  This is too late/hot in my opinion, so here is an easy way to add a manual switch to operate the fan.
The fan controller is located under the drivers side of the dash, below the headlight switch.
The controller is easily removed from under the dash to get the connector removed from the controller.
There is the controller held by 2 screws.
Notice the switch at the top of this image, I mounted it in holes that were already in the bottom of the dash.
The modification is easy, you need a switch that can handle the amp load of the fan (20A?), two wire splices (yellow for 10ga wire), and some 12-14 ga wire.
Unfortunately, I did not use the yellow wire splices, but I will replacing them very soon.
A up-close look at the connector.   There are 8 wires attached to the connector.  Wire 1 is on the left.   Attach the splices to wire 5 and wire 8.  Then attach the switch to the added wires.
Wire 5 is brown with a yellow stripe (BR-Y) and Wire 8 is grey with a yellow stripe (GY-Y)
The schematic taken from the Ford manual, shows that wire 8 could be O-BK or GY-Y.
So what does this do?  Actually you are connecting the Hot in Run wire (wire8) directly to the Fan wire (wire5).  This eliminates the controller.
Here is the fan controller circuit.   Click on the image to get the full size image.
Good luck!  I am not responsible for any problems associated with this modification.  This is only showing what I did to manually operate the fan.

Additional note from Carl Morris: If you don't mind your computer thinking the engine is very hot (it may not allow maximum power), you can also cause the fan to come on by attaching a wire to the yellow wire with a red stripe (signal 45) going into the fan controller, and switching it to ground. This wire is in the lower right of the schematic shown above with the number 45 next to it.