How to Hook a Four Flat Trailer Harness to a Five Flat Wire Harness

The law requires only four lighting functions to tow a small, light-weight trailer.

Small, light-weight trailers with no brakes typically have wiring harnesses which terminate in a 4-flat trailer harness, properly called a flat four-pin hitch. This style hitch supplies electrical signals to the legally mandated minimum functions, being tail lights, brake lights and both turn signals. A 5-flat harness, properly called a flat five-pin hitch, fitted on a tow vehicle provides those basic functions and one other line, typically carrying current from the tow vehicle's backup lights to a surge braking system to disengage the trailer brakes when reversing. A converter is required to tow a trailer with a 4-flat harness using a tow vehicle equipped with a 5-flat harness.

Difficulty:

Easy

Instructions

Things You'll Need

• Converter

1. Obtain a converter which has a female flat four-pin receiver at one end and a male flat five-pin plug at the other.

2. Press the female flat four-pin receiver over its male counterpart on the end of the trailer's harness.

3. Press the male flat five-pin plug into its female counterpart on the end of the tow vehicle's harness.

References

• Horse Trailer World: Trailer Wiring Tips
• Etrailer: Adapter 4 Pole to 5 Pole Wiring