The four-pin relay is generally composed of an iron core, a coil, an armature, and a contact reed. As long as a certain voltage is applied to both ends of the coil, a certain current will flow in the coil, resulting in an electromagnetic effect, and the armature will overcome the pulling force of the return spring and attract to the iron core under the action of electromagnetic attraction, thereby driving the armature. The moving contact and the static contact (normally open contact) are pulled together. When the coil is powered off, the electromagnetic suction also disappears, and the armature will return to the original position under the reaction force of the spring, so that the movable contact and the original static contact (normally closed contact) are released.

In this way, the suction and release are achieved, so as to achieve the purpose of conducting and cutting off in the circuit. For the "normally open and normally closed" contacts of the relay, it can be distinguished as follows: the static contacts that are in the open state when the relay coil is not energized are called "normally open contacts"; the static contacts that are in the connected state are called "normally open contacts". It is "normally closed contact". A relay generally has two circuits, a low-voltage control circuit and a high-voltage working circuit. The four-pin relay 85.86 has two feet of small current and small magnetic attraction, and the other two feet are connected to the high current line.