What are the Functions of a 4-Way Flat Trailer Wiring Connector with 5 Wires

Question:

5 wires into a 4 flat connector. The connector was damaged. Since 5 wires end up in 4 flat connector, which 2 wires occupy a common pole on the 4 pole flat connector?

asked by: Marki

Expert Reply:

What you are describing is called a wishbone harness. This is different than a 5-Way flat connector like # A40W5B that you have referenced. A wishbone harness will have 5 wires, 2 of them going to the running light pin which is right next to the ground pin. This is so you do not have to splice in a jumper wire to go from one tail light to the other for the running light function.

A 5-Way flat will have 5 wires (though there are also wishbone 5-Ways) and the extra pin is usually attached to a reverse electric backup solenoid on trailers with surge couplers. On the vehicle side this 5th pin would be connected to the reverse light circuit on the vehicle. When the vehicle is placed in reverse it powers the solenoid on the coupler and allows you to back up without the brakes engaging.

expert reply by: Michael H