How to Wire a 7 Pole Trailer Light Plug

Large trailers, such as this RV, typically require a seven-way trailer outlet.

A large trailer–such as a horse trailer or recreational vehicle–requires extra lighting and trailer brake controls. For this reason, large trailers require more electrical connections than a simple four-way trailer outlet can provide. A large trailer may require a seven-way (also known as a “seven pole”) trailer outlet. To wire such an outlet on the towing vehicle, the towing vehicle must have an electric trailer brake system currently installed.

Things You'll Need

• Wire-splice terminal connectors
• Screwdriver
• Electrical wire
• Crimp-style spade connector
• Electrical pliers
• Slip-joint pliers or adjustable wrench
• Seven-way round trailer harness

Instructions

1. Loosen and remove the taillight lens retaining screws. Pull the taillight frames on each side forward to expose the taillight wires. Each wire is labeled as to which light it actuates.

2. Place the first splice connector over the wire marked as the left-turn signal wire. Insert the yellow wire from the trailer harness into the splice connector. Crimp the splice connector to connect the wires.

3. Slip the second splice connector over the wire marked as the right-turn signal wire. Insert the trailer harness green wire into the splice connector. Crimp the splice connector to connect the wires.

4. Slip the third splice connector over the wire marked as the parking-lamp wire. Insert the brown wire from the trailer harness into the splice connector. Crimp the splice connector to connect the wires.

5. Place the fourth splice connector over the wire marked as the ground wire. Insert the trailer harness white wire into the splice connector. Crimp the splice connector to connect the wires.

6. Place the fifth splice connector over the wire marked as the trailer brake wire. Insert the blue wire from the harness into the splice connector. Crimp the splice connector to connect the wires.

7. Place the sixth splice connector over the wire marked as the backup light wire. Insert the purple wire from the trailer harness into the splice connector. Crimp the splice connector to connect the wires.

8. Run a length of wire from the positive battery terminal to the rear bumper. Route the wire so that the wire does not catch on any moving parts. Using the electrical pliers, strip ½ inch of insulation from the battery end of this wire. Place the spade terminal over the wire, and crimp the spade terminal to the wire. Using the adjustable wrench or slip-joint pliers, loosen one of the top bolts on the positive battery terminal, and place the spade terminal between the bolt head and the battery terminal. Tighten the top bolt until it holds the spade terminal snugly.

9. Slip the seventh splice connector over the wire that runs to the positive battery terminal. Insert the harness black wire into the splice connector. Crimp the splice connector to connect the wires.

References

• ETrailer: Trailer Wiring Diagrams