S14 factory fan? theres 4 wires (yellow, black, green & blue)

yellow and black are grounds

green and blue are powers

use any one combination (yellow and blue, green yellow, etc) and the fan will run on low speed

but use all 4 wires, and its on high speed. you can just ground out the yellow and black wires and then run the green and blue jointly through the relay and it will run on high. a relay has 4 posts on it. one is ground. one is trigger, and the other 2 are the actuall switched wires. the battery is connected to one side and the fans; the other.

when the trigger is powered (IG +), it energizes a solenoid that connects the switch inside bridging the power from the battery to the fans. the simple is best complimented with a thermostatic switch that energizes the relay only when the coolant temps need it.