Relays most cars can find the relays by lifting the hood and finding the relay box. Control relays are used in automobile lighting, wiper, starter, air conditioner, electric seats, electric doors and Windows, anti-lock device, suspension control, acoustics, etc. It is one of the most used electronic components in automobiles. At present, global market demand exceeds 1 billion annually. The control relay has two main parts, one is the control system and the other is the controlled system. Control relay control can, because when it's some kind of signal in the control system, such as electricity, magnetic, heat, light and other physical quantity reaches a certain value, can make the controlled system (also called the output circuit) controlled by the amount of mutation from zero to a certain value, mutation or by a certain value to zero, so as to achieve control, protection, information transfer and conversion, and so on. Controlling large current with small current is the characteristic of controlling relay. Automobile control relay technology requires harsh requirements, because it needs to adapt to vibration, high temperature, low temperature, humidity, and corrosive and harsh environment such as oil, salt and water. It requires long life, high feasibility, small volume and low consumption, as well as electromagnetic compatibility, flame retardancy and fast response speed. It can be said to want horses to run, but also want the horses do not eat grass. As a vehicle control relay, it must meet these requirements. At present, automobile control relay is mainly mechanical, but it has developed to solid state relay. When the relay malfunctions, it can immediately paralyze the system's components and even cause the entire car to freeze. For example, if the starter relay fails, the car cannot start on electricity. Although the starting relay costs more than ten yuan a piece, the car cannot run without it.