How to Convert a 5-Pole Flat Trailer Connector to 4-Pole Flat Connector

Updated 06/04/2020 | Published 11/03/2009

Question:

2005 Ford Explorer. I have a Boat trailer with a damaged 5 pole that I would like to convert to a 4 pole. What do i do with the Yellow/Brown wire on the 5 pole? Thanks

asked by: Mark A

Expert Reply:

Some 5-Pole flat connectors use a total of 6 wires. They operate as follows:

Blue - trailer brakes
Green - right hand brake and turn signals
Yellow - left hand brake and turn signals
Brown/Green - right hand running lights
Brown/Yellow - left hand running lights
White - ground

The brown wires with the yellow and green tracers or stripes are the same circuit. They provide power to the side markers and taillights when the vehicle headlights are on. When converting these to a 4-Pole, the two brown wires should just be spliced together and connected to the plain brown wire on a 4-Pole. Some 5-Pole connectors only use 5 wires and would be color matched to a 4-Pole connector while omitting the blue trailer brake wire.

Wiring for a 4 pole is as follows:

White - Ground
Brown - Taillights also known as Running Lights
Yellow - Left Hand side brake and turn
Green - Right Hand side brake and turn

The added wire, usually blue, on a 5-Pole is usually for trailer brakes, since you have a boat trailer, that blue wire may be for charging a trolling motor battery.

If you do not need that 5th wire anymore, I would just remove it and use a 4 pole connector like part # 18004.

If you want to retain the 5th wire, we do have 5 pole wiring parts. I have included a link to the page with our 5 pole flat parts and our 5 pole round.

expert reply by: Patrick B

W. P.

6/1/2020

2007 Toyota extra cab longbedv4x4 I have tried to connect a 4 flat trailer connector to a 5 flat connector and it's not working properly. Connecting green to free ,yellow to yellow and the three brown wires together. Once that's completed all is well but the right turn signal doesn't blink and is deem. What am I doing wrong? Thank you for you assistance.

Chris R.

6/4/2020

The dim light you mentioned sounds like a bad/weak ground. I would definitely start by making sure the harness is properly grounded on the trailer frame (make sure it's a clean, bare piece of metal). Let me know if this doesn't fix the issue.