The wiring of each pin of the 4-pin relay in the automotive relay

①Normally open contact: Pins 85 and 86 are internally connected to the coil, and externally connected to the control terminal, such as switches, output control signals, etc.; pins 30 and 87 are internally connected to the contacts and externally connected to the load. When there is voltage at both ends of the coil and the voltage reaches the pull-in voltage, the two contacts are closed, the circuit where the load is located is turned on, and the load starts to work.

②Convertible contact:
a. Pins 85 and 86 are connected to the coil. If only pins 30 and 87 are connected, and 87a is left empty, it is the same as the normally open contact;
b. If only pins 30 and 87a are connected, and 87 is left empty, it becomes a normally closed contact relay, and the working principle is opposite to that of normally open, that is: when the coil reaches the disconnecting voltage, the contact is disconnected and the load stops working;
c. In order to form a circuit, the pins of the three contacts can be connected to achieve different functions. Generally, it is a combination of multiple channels. This method of use is common in twin relays.