I do not understand why you want to change a working system. It goes automatically at that speed what is needed. If you have it on all the time, it will cool too much.
Even the fan with the visco clucth you normally do not need when driving at highways with moderate speed, because there is enough wind which goes thru the radiator.
That is called a ballast resistor, a high-power low-value resistor in-line with the fan.
Its purpose is to give the fan 2 speeds, one high speed when the resistor is out of the circuit, and one low speed when the resistor is in the circuit. That is when there is also two thermal sensors attached to the radiator.
Brown wire (always brown) for ground.
The other two wires are one for the stage 1 speed, the other for stage 2 speed.
Pick one and apply 12V, you can tell if it works, it is pretty loud.
To check high fan speed, remove plug to temp sensor and bridge the 2 pins in the plug (with ignition switched on).