The five pins of the five-pin relay on the car are 30/85/86/87/87a, one is the power supply line, two are the control line, and the other is the output line. The specific operation steps for each pin are as follows:

1. 30 is the main power input, which is connected to the power cord from the vehicle fuse.
2. 85 is the power input terminal of the control line, that is, the connection to the vehicle switch.
3. 86 is the ground terminal of the control circuit, that is, the negative terminal of the vehicle.
4. 87 is a normally closed pin, that is, it is connected to 30 when it is not powered on, and it is disconnected when it is powered on.
5. 87a is a normally open pin, which is disconnected from 30 when it is not energized, and connected to 30 when it is energized.
We choose to use the "Normally Open Normally Closed" pins as needed. After the 12V DC is turned on, we will hear the sound of the relay "carding", indicating that it is working properly.