All other trailers will have the larger 7-way plug which accommodates electric brakes and has a separate line for inside lights.
It is important to add a ground wire running from the plug back to the frame of the tow vehicle. Safety chains, hitches, couplers, and load levelling equalizer bars will NOT provide an adequate continuous ground and are the cause of many electrical failures. In addition, any hot line or auxiliary line should be run with an inline fuse.
If an auxiliary battery is added to the trailer, there must be a fuse installed between the battery and the load.
