In the following diagrams there are two sections:
Internal section reflects a simplified version of the on-board circuit. The External section reflects the wiring that the user can build.
Bi-directional Opto-coupler Input
The LOAD element in the following diagrams can be a motor, a light bulb, a heating element or something else.
The DC Source polarity doesn’t matter from the Relay Output point of view, it can matter for your load. The positions of the LOAD and DC Source can be interchanged.