- 1). Locate the wiring which serves the trailer's electrical functions, colloquially called the pigtail. It should be attached beneath the trailer tongue, secured in place with plastic zip ties, and is normally bound with electrical tape or spiral trunking. The pigtail will comprise seven wires on trailer equipped with electric brakes, and four wires on a trailer equipped only with lighting circuits.
- 2). Inspect the terminal at the end of the pigtail, properly called the trailer hitch. A four-wire pigtail will have a flat four-pin hitch attached, and a seven-wire pigtail will have a round seven-pin hitch attached.
- 3). Fit the trailer's hitch into the matching outlet component on the tow vehicle, which is usually located adjacent to the tow package by manufacturers and installers. Separate a cap from a four-pin outlet or raise a sprung cover from a seven-pin outlet, then slide the hitch into the outlet until a positive resistance if felt. Four-pin hitches typically have no locking device, and seven-pin hitches are typically held in place by lowering the sprung cover until a tooth on its underside mates with a notch on the outer case of the hitch.
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