WARNING
Safety chains, hitches, and couplers do not provide adequate grounding by themselves and can cause electrical failures.
You must have the correct vehicle wiring when using your trailer. Trailers not equipped with brakes will have a 4-way flat plug and all other trailers will have a larger 7-way plug. Don’t forget that a ground wire running from the plug back to the frame of the tow vehicle must be incorporated into proper tow vehicle wiring. Below are diagrams of the 4-way and the 7-way plugs.