1. Find the coil pin.

Use a multimeter to measure the resistance between the pins. The two pins with a resistance value of about several hundred to 1K ohms are coil pins. Note that the coils of some relays are divided into positive and negative poles. Although the reverse connection will not damage it, it will not operate.

2. Find the normally open and normally closed points.
Use a multimeter to measure the pins other than the coil, the two conducting pins are normally closed, add 5V DC to the coil to make the relay act, they should be disconnected; if they are not disconnected, they are short-circuited internally .

Add 5V DC to the coil to make the relay act, and then use a multimeter to measure it. If there are two pins that were not connected, they are normally open.

The pin that is related to both the normally open point and the normally closed point is the common terminal.
On the side of the three feet, the middle pin 2 is the common terminal of the output contact, and the other two pins 1 and 3 are coils, that is, connected to the driving end. Pins 4 and 5 are normally open and normally closed contacts respectively.