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Wiring New 4-Way Connector on Trailer with 5 Wires  

Updated 09/16/2025 | Published 06/18/2015

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Question:

what do color wires go to. i have on boat trailer green,white,yellow, brown with green, and brown with yellow. trying to hook to 4 flat connector

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Expert Reply:

Going by the colors that you mentioned, it sounds like you have the typical set-up, green wire for right turn and brake, white wire for ground, yellow wire for left turn and brake, brown with green wire for right side running lights, and brown with yellow for left side running lights.

If you are using a standard 4-flat connector like part # 18004, you will more than likely be able to connect color for color for the green, white, and yellow wires. As for the brown with green and the brown with yellow, these will both need to be connected to the brown wire on the new connector.

Please keep in mind that trailer wiring colors can vary so wiring by function really is the best way.

expert reply by:
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Leah S
David R. profile picture

David R.

1/12/2021

I have a Mazda Miata with the standard 4 pin connector and i Have a small cargo trailer that has 7 wires (2 red, 2 brown, 1 green,1 white and 1 yellow) that I don't understand. What kind of connector or harness do i need to buy from you. Any help is appreciated

Jon G. profile picture
Etrailer Expert

Jon G.

1/18/2021

Does your cargo trailer only have bare wires and no connector? I would guess that your red wires are brakes, brown are running/tail, green is right turn, white is ground, and yellow is left turn. Typically stop and turn signals are combined on a trailer so if you want to go that route let me know. You will either need to find a wiring diagram for your trailer or test your wring with 12V power to verify the functions of your trailer wiring. There are common wire colors for functions but it's always best to double check by testing. Let me know what you find and we can go from there.
Richaed L. profile picture

Richaed L.

7/29/2024

thanks for the reply. that is what i assumed but i just needed confirmation

Jeffrey B. profile picture

Jeffrey B.

4/20/2025

Have LED lights that has red yellow white green and gray how do I hook that up to a trailer with a 4 pin

Jameson C. profile picture
Etrailer Expert

Jameson C.

5/5/2025

@JeffreyB Each light has that many wires? I would assume the white is ground and then use a jumper wire from a 12 volt battery to test the rest of the wires to see what activates and then wire to 4-way accordingly. Traditional 4-way wiring is white ground, brown running light, green right turn stop, and yellow left turn stop.
Mike B. profile picture

Mike B.

7/8/2025

Will the hot wire on a 7 way adequatly charge a 12v battery?

Jerred H. profile picture
Etrailer Expert

Jerred H.

7/8/2025

@MikeB A vehicle 7-way connector won't charge a dead battery, but it will keep the battery topped off when you are towing the trailer. We call this a maintenance charge. You're going to need to install a battery charger like the Redarc In-Vehicle BCDC Battery Charger item # 331-BCDC1225D in order to actually charge your trailer battery.
Bobby profile picture

Bobby

8/27/2025

Good morning I have a highway cargo by Carson trailer and it has five wires green/brown and yellow/brown and a white wire . I’m trying to hook up a four pin connector that has four wires, green, white, yellow, and brown. Could you please help me what is the correct way to wire it up

Nick S. profile picture
Etrailer Expert

Nick S.

8/28/2025

@Bobby Hey Bobby, going from a 5 wire system to a 4 wire you simply will just splice the brown wires together as they are the same function, and then color match the rest as they are.
Jd profile picture

Jd

9/15/2025

Tried that Leah. Still have no turn signal on the right. Bulb has been replaced. I have tail lights, brake lights, and left turn signal only.

Robin H. profile picture
Etrailer Expert

Robin H.

9/16/2025

@Jd check your vehicle and make sure it is sending power on the right turn circuit, then check your trailer wiring for power and work your way back. Could be a short, bad ground, vehicle or trailer side. If it is on the trailer side and you aren't able to find the short it is best to just run new wire.

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