The first ever relay was invented in 1835 by an American scientist by the name of Joseph Henry. From the time of its inception until today, the relay has become a common component in many devices. The main purpose of relays is to control the flow of large currents by means of using only a small amount of current. Earlier application of relays was in communication but was later on replace with digital equipment. Relays were also use to protect motors by switching them on or off thereby preventing these motors from overheating. In vehicles, relays are use to operate some of the components inside the vehicle such as the a/c, wiper, radiator, and others. When it comes to relays, you can trust the Kaehler brand. It is a renowned relay brand and trusted by most DIY communities around the globe.A Kaehler relay is famous for its excellent quality and durability. These qualities have helped the brand to become one of the most sought after relay brands in the world--with special mention to its a/c relay and wiper relay. The a/c relay acts like a switch and transfers power from the interior a/c controls of a vehicle to the a/c compressor. The typical a/c relay in an a/c control installation include a three-wire connection wherein one wire is used as ground, another wire is use as the input wire from the interior control panel and switches while the last wire serves as the power feed to the a/c compressor clutch.The main purpose of the wiper relay is to control the function of the windshield wipers hence once the relay fails the wiper also fails. When this happens, you would need to replace the relay as soon as possible or you'll end up driving without a wiper. Now, we all know the discomfort of not having a working wiper-the windshield can get so dusty to the point that you can't see what's ahead. It's scary because it can lead to accident so replace the relay immediately. The wiper relay is located in the power distribution box underneath the hood.