Last week we talked about the standard DIN numbers used on relays and the incredible utility they represent. With that understood, you can easily troubleshoot any circuit that uses a relay. For those who prefer the left-brain, lay-it-out-in-a-table approach:. Output to other device, normally closed, pulled open when coil is energized. When troubleshooting relay-related wiring, you need to be very clear about the DIN numbering and not confuse the numbering on the underside of the relay with the numbering on the socket the relay plugs into. They are the mirror-image of each other.
Let's discuss how to wire a relay and go through the concepts of how a relay works. A relay is basically a switch but not like a switch that's on a wall. A wall switch relies on someone to flip it which will then control a light or some other type load. A relay is switched by electrical power and not a human.
Every circuit added to a modern car should be run through an automotive relay. The factory wiring in modern cars is light gauge, and is not designed for additional loads. A relay can be used to power a new circuit with very little added current draw on the original wiring.
A relay is essentially a switch that is operated electrically rather than mechanically. Although there are various relay designs, the ones most commonly found in low voltage auto and marine applications are electro-mechanical relays that work by activating an electromagnet to pull a set of contacts to make or break a circuit. These are used extensively throughout vehicle electrical systems. This is the most common reason and useful where an in-line switch or the existing circuit does not have the capacity to handle the current required.