Why Would Trailer Wiring 4-Way Have 5 Wires Ran to It

Question:

Bought a 4 prong harness but it has 5 wires and the trailor only has 4. White, yellow, green, brown. The harness has the same but an additional red wire. Hooked the four up, lights do not work.

asked by: Juanita C

Expert Reply:

Typically a 5th wire ran to a 4-way harness is either a wishboned running light circuit where each side of the trailer's running lights are ran to either wire or it's a case where there is two ground wires. Since you said none of the circuits are working that to me says it's a ground circuit that needs to be ran to the same circuit as the white wire. But you can test this by jumping a 12 volt circuit to the red wire and see what happens. If there's a spark as they touch it's ground. If a different circuit lights up that answers that question as well.

We have wishbone 4-ways like the part # A20WB which comes with 30 feet of wire.

expert reply by: Jameson C