The video below explained us about how to wire a relay. We already know that there are two components inside a relay, switch and an electromagnet. Here’s how to wiring a relay.
First, put the negative or ground to one into the magnet. Second, put on other wire to power switch inside the car to the positive of the magnet. Then you can check that the relay is working. Third, just put the electric fan into the relay then you can control the fan on or off from the switch. For further information about relay wiring, watch the video.