Autozone has the schematic wiring diagram on their site which shows the resistors. The resistors are for the (3) speeds. The fans are controlled by a computer that has various inputs and will control the fan(s) speed. The resistors are designed for (2) fans wired together and may not operate properly with (1) fan.
If you do not have AC you can control the fan using a relay kit from Summit which includes the temperature sensor and a relay.
The black/pink wire from the fan motor is the high speed wire. Connect this wire to the relay kit. The black wire from the motor is ground. The resistor is for low and medium speeds. The black/red wire is for low speed. The red/black wire is for medium speed.