How to Install a Four Prong Trailer Wire Harness

Trailer harnesses tap the rear signal wires.

Trailers must be connected to the automobile's signaling system. Depending upon the type and size of trailer, the interface at the automobile side of the electrical circuit may require four, five, six or seven prong pins. One of the most common ways to connect a trailer to the automobile signaling system is by means of a four wire (or four pin) electrical harness.

Things You'll Need

• Wire splice connectors (4)
• Four pin automobile wire harness
• Electrical pliers
• Phillips head screwdriver

Instructions

1. Loosen and remove the rear signal lamp covers to expose the rear signal wiring. Slip the first splice connector over the right turn signal wire. Insert the green wire from the trailer harness into the splice connector and crimp the splice connector onto the wire pair.

2. Slip the second splice connector over the left turn signal wire. Insert the yellow wire from the trailer harness into the splice connector and crimp the splice connector onto the wire pair.

3. Position the third splice connector over the tail lamp wire. Insert the brown wire from the trailer harness into the splice connector and crimp the splice connector onto the wire pair.

4. Slip the fourth splice connector over the ground wire. Insert the white wire from the trailer harness into the splice connector and crimp the splice connector onto the wire pair.

Tips & Warnings

• Each wire is typically marked with an indicator tab at the tail lamp bulb connection.

References

• Champion Trailers: Four Pole Flat Trailer Wire Diagram
• Horse Trailer World: Trailer Wiring Tips

Resources

• AutoZone