A trailer has a 12-volt electrical system powered by the tow vehicle and transferred to the trailer via a 7-pin connection in the vehicle's hitch that provides electricity for turn signals, brake lights, marker lights, electric brakes, batteries and reverse lights. These systems are required by law in every state to tow on public roads; the lights provide other drivers with information regarding the size, turning indications and potential slowing of the trailer.
Attach the 7-pin harness to the trailer's tongue with a cable tie. Provide just enough cable length so that the harness can connect to the vehicle without dragging on the ground.
Remove a very small area of paint from the trailer's tongue with sandpaper. Fasten the white wire from the harness to this location with a self tapping screw and drill.
Run the green wire down the right-side fame rail and connect it to the right taillight's power wire with a scotch lock connector. Place each wire in one groove of the connector and close the gate. This forces a metal blade into each wire, creating a connection.
Run the yellow wire down the left-side fame rail and connect it to the left taillight's power wire with a scotch lock connector.
Run the brown wire down the left side of the trailer to the first marker light. Connect it to the corresponding power wire with a scotch lock connector. Keep running the brown wire around the trailer, connecting it to each marker light in the same fashion.
Run the blue wire to the trailer's electric brakes and connect it with a scotch lock connector.
Run the red wire to the trailer's battery. Loosen the positive terminal of the battery and slide the red wire underneath. Re-tighten the terminal down to hold the wire securely.
Run the purple wire to the left taillight and connect to the backup light's power wire with a scotch lock connector. Continue running the purple wire to the second taillight and connect to its backup light using the same method.
Wrap all of the connections very tightly in electrical tape. Attach any loose wires to the trailer's frame with cable ties.
