The system is very simple.
You have 2 relay in the fuse box. They are id as Rad Fan. The one nearest the shock tower is the Lo speed one. The middle one is the hi speed one.
The Lo speed relay is activated by the sensor in the bottom of the radiator. It is a 2 wire connector) It start at 185f and stop at 172f.
To go lo speed, the negative wire of the fan is bypass via the fan resistor (bolt on fan housing).
The high speed relay is ativated by the sensor behind the thermostat housing. It is a 1 pin sensor with a Blue wire with a black line on it. It start at 215f and stop at 206f.
If you want to have the hi speed relay activated at on switch position, just unconnect the connector from the 1 pin sensor with a Blue wire with a black line on it behind the thermostat housing and put it to ground.
If you want to have the lo speed relay activated at on switch position, just unconnect the connector from the 2 pin sensor on the radiator, just made a jumper between both pin.
In both case, fan will start at on position because the positive activation of the relay is only powered at on position.
Me what I do is to use 2 fan in High speed. I do not have no more AC.
I want to use AC fan as first to start (To force air to pass true the rad to prevent turbo to heat-up the rad) so i leave the hi speed system to start the Pull fan when temperature hit 215f in the engine.
And i modify the lo speed relay system to start the pull fan (AC oem one)but at hi speed.
I remove the 3 srew that hold the fuse box to acces the wire under the fusebox.
I cut the 2 wire of the lo speed relay (Blue wire with white line and cut also the blue wire) Carefull, both lo & hi speed relay has the blue wire with white line.
Insulate the 2 wire you just cut that go in the wire hardness to prevent short.
Then use the 30a fuse of the AC to feed the AC fan. You cut the Black wire with white line and bring it to the blue wire of lo speed relay, then pass a new wire from the blue wire with white line of the lo speed relay and bring it to the fan.
You cut both wire of the fan, plug the new wire and the other wire of the fan, just put it to ground.
Again, insulate the 2 old wire of the fan to prevent short.