As illustrated in the wiring diagram, a four-pin relay uses two pins to control the coil and two pins that switch power on a single circuit. The following relay diagram shows that there are two types of four-pin relay -- normally open or normally closed. As the wiring diagram illustrates, a normally open relay will switch power ON for a circuit when the coil is activated. Whereas normally closed relays default in the closed position, the circuit is closed unless otherwise specified. With the help of EdrawMax, you can easily create such complex 4-pin relay diagrams for your professional usage.