The four-pin relay is similar to the five-pin relay, and there is a structural schematic diagram on the side. The wiring method is as follows:

The two terminals are pins 85 and 86. It can be known from the side structure diagram that these two terminals are used to control the electromagnetic pull-in and disconnection, so one end is usually connected to the positive pole of the power supply, and the other end is connected to the low-side drive output lead. foot.
The two terminals are pins 30 and 87, of which pin 30 is the normally closed end and pin 87 is the normally open end. Therefore, pin 30 is also connected to the positive pole of the power supply, pin 87 is connected to one side of the load, and the other side of the load is grounded.
85 and 86 are the input terminals of the relay start signal (small current input), 87 is the output terminal (large current outflow terminal), and 30 is the source of high current supply (usually connected to the positive pole of the battery), when 85, 86 When there is a signal (power on), the relay will connect 87 and 30 at this time, so that a large current will flow out from 87. If there is no signal at 85 and 86, then the 87a end will be connected to 30.