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What are the Functions of a 5-Way Flat Trailer Connector with 8 Wires


I have a 5 way flat connector from my boat that is equipped with 8 wires. 2 white, 2 brown 1with green stripe, 1 yellow, 1 green, and 2 reds. Why do I have so many wires and how can I convert this to a 4 way plug? Thanks for your help


Expert Reply:

On a 5-Way trailer connector, usually found on boat trailers, the pin on the end furthest from the ground pin is used on an electric reverse lockout on the trailer coupler. This is so when you put the vehicle in reverse, it will single a solenoid on the coupler and not allow fluid to go back to the brakes so you can back up without the brakes engaging. If this is what is on your trailer then you would not want to switch to a 4-Way connector unless you also switched to free-backing brakes.

It sounds like the 8 wires on your connector are as follows:

Running light circuit (split into 2 wires at the plug)
Left turn
Right turn
Brake lights (possibly split at the plug)
Output to reverse lockout

The colors I cannot verify because there is no universal color code for trailer or vehicle wiring. On a normal 5-Way on a trailer the covered pin is ground. then the running light pin, followed by the left turn/brake signal, then the right turn/brake signal, and last is for the reverse electric lockout.

It seems as though the harness was wired either because a tow vehicle had a connector with separate brake and turn signals so the trailer side was wired to match or that someone did not want to run jumpers from one side to the other so it was done at the plug rather than further back at the trailer.

You will want to trace the wires back from the connector to see where they go to determine functions. I recommend wiring it up the traditional way described above and in the wiring FAQ I have linked (again go by function, not color) using harness # A40W5B.

Then, if the trailer does have an electric reverse lockout add a 4 to 5-Way adapter to the vehicle using # 20036.

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