How to Wire a Six-Pin Trailer to a Seven-Pin Truck

A trailer that is not matched to the truck is a simple problem to get around.

Tow vehicles in the U.S. are typically fitted with either a flat four-pin electrical type connector or a round seven-pin electrical type connector. The four-pin units control sidelights, brake lights and turn signals and provide a ground connection; the seven-pin units control those functions plus electric brakes, a 12-volt hot supply and an auxiliary wire. A six-pin trailer connector normally does everything that a seven-pin unit does, except transfer the auxiliary signal.

Things You'll Need

• Screwdriver
• Round seven-pin connector

Instructions

1. Remove the outer case from the six-pin trailer plug -- typically, a single screw in the side of the case holds it in place; use a screwdriver to retract the screw by turning it counterclockwise, then slip the case down the wire a little.

2. Use the screwdriver to release all the screws that hold the six wires in place inside the hub of the six-pin connector. Again, rotate the screws counterclockwise to undo them. When the screws are all loosened, pull the six wires from under the six screws, then slip the case of the connector up and off the wire.

3. Remove the outer case from a round seven-pin trailer plug as described in Step 1. Slip the case -- small-end first -- down the wire from the trailer. Use the screwdriver to loosen all six terminal screws around the periphery of the hub of the seven-pin connector -- there must be sufficient space between the bottom of each screw and the steel terminal plate beneath it for a single piece of wire to be installed. Leave the central screw untouched.

4. Insert each of the six wires into a numbered terminal, working one wire at a time, and tighten the terminal screw by turning it clockwise. The numbered screws correspond to the colored wires as follows: White wire to terminal one; blue wire to terminal two; brown wire to terminal three; black wire to terminal four; yellow wire to terminal five and green wire to terminal six. Terminal seven, the central screw, remains unoccupied.

5. Slip the case of the round seven-pin connector back up into position -- this usually requires a small tooth be aligned with a small rebate -- and tighten the retaining screw. Press the new connector into the seven-pin receiver on the tow vehicle and test all electrical functions.

Tips & Warnings

• Six-pin connectors are old-fashioned and outdated, but used commonly on horse trailers. Some specialist horse trailer dealers may still have old stock six- to seven-pin converters. If you can find one, these simply press into the seven-pin socket on the tow vehicle and then accept the six-pin connector from the trailer. This negates any need for the electrical work described.

References

• eTrailer: Wiring FAQs