Follow this link for information on The Different Types of Relays and how they work.
You can think of a Relay as a remote-controlled switch where a low-amperage signal controls a high-amperage output.
- Pin 30 is the high-amperage input.
- When a positive control signal is present at pin 86 and pin 85 is grounded, pin 30 becomes connected to pin 87 inside the relay.
- When power to pin 86 or ground at pin 85 is removed, the connection between pin 87 and 30 is broken.
The way most people think about a relay is positive output/positive control. The example below is for a fuel pump.
This is just one way to wire a relay. They can also be controlled through the ground. The next example shows an electric fan controlled by a temperature switch. It provides a ground when the engine gets hot.
The high-amperage input and output don’t have to be positive. A relay can just as easily provide the ground for the high-amperage circuit. Just like the previous examples, they can be controlled with the ground at pin 85 or the positive at pin 86.
Relays aren’t limited to controlling just the devices in the examples above. These configurations can be used to control almost any device. The main consideration is keeping the high-amperage wiring as short as possible.