How to Wire a 7-Way Trailer Plug (It's Easier Than You Think)

7-ways are some of the most common harnesses found on trailers. 7-ways provide the required running lights, turn signals, brake lights, and ground for the trailer. In addition, they provide three additional pins for a 12V hot lead, electric brakes, and reverse lights.Trailer wiring can be one of the most intimidating components of your towing setup, but it doesn't have to be. Most of us aren't electricians, but that doesn't mean wiring a trailer is beyond us. We'll walk you through the trailer-wiring process for 7-way plugs below, so you can get your trailer up and running in no time.
Watch video installation of 7-way connector (vehicle end)
Watch video installation of 7-way connector (trailer end)
7-Way Round Connector

What is the Color Code for 7-Way Trailer Wiring?

Before we get into the step-by-step walkthrough, we'll first go over the standard color code for 7-way wiring harnesses. This will make it easier when it comes time to make your wiring connections.The color code for wiring harnesses varies between industries. In particular, SAE (Society of Automotive Engineers) standard wiring differs from the RV industry's standard wiring. The standard for both is as follows:SAE Standard
  • Green: Right turn/brake light
  • Yellow: Left turn/brake light
  • Brown: Tail/running lights
  • White: Ground wire
  • Blue: Brake controller output
  • Black: Battery hot lead
  • Purple: Reverse lights
RV Standard
  • Green: Tail/running lights
  • Yellow: Reverse Lights
  • Brown: Right turn/brake light
  • White: Ground wire
  • Blue: Brake controller output
  • Black: Battery hot lead
  • Red: Left turn/brake light
What Size Wire Gauge is Used for a 7-Way Wiring Harness?The minimum suggested wire size for a 7-way trailer plug is 16 gauge for the turn signals, brake lights, reverse lights, and running light wires. The suggested minimum for the ground, brake power, and battery hot lead wires is 12 gauge.
7-Way Flat SAE Connector Diagram
7-Way Plug RV Standard Diagram
7-Way Plug Heavy Duty Diagram
7-Way Trailer Wiring Color Code Traditional SAE
7-Way Trailer Harness Diagram - Traditional SAE
7-Way Trailer Wiring Color Code RV Standard
7-Way Trailer Harness Diagram - RV Standard

Wiring a Trailer with a 7-Way: Step by Step

Now that we have an idea what our wires do, let's get into the step-by-step process of wiring your trailer with a 7-way connector.

Trailer Side

Step 1: Prepare for Trailer Wiring Installation

Start by making sure you have everything you need to wire your trailer, such as:
If you need to replace one or more of your lights, you can purchase trailer lights or use a complete trailer light kit, which will come with the necessary wiring included. Remove old lights before beginning the new installation.If you don't need to replace your lights, you can simply use a 7-way harness.
Trailer Junction Box
Pictured: junction box

Step 2: Locate or Install Junction Box

If you're replacing existing wiring and your trailer already has a junction box, locate it (it's typically near the front) and remove the cover. Remove the nuts from each terminal.If you're installing a new junction box, find a suitable location for installation, such as on the inside edge of your trailer tongue. The box should be close enough for your wires to reach, but away from any components it could interfere with.If you don't have a junction box and don't want to install one, you can simply tie the new wiring harness in with your trailer's existing wiring.
Junction Box on Trailer
Locate the junction box and remove the nuts from each terminal.

Step 3: Make Trailer Connections

NOTE: Check the manufacturer's instructions for any wiring harness you use. The instructions will identify the function of each wire. You won't always be able to rely on color alone to match up wire functionality.
WITH JUNCTION BOXIf you have a junction box and are simply adding a new 7-way connector, remove the nuts on each junction box stud. If you're replacing existing wiring, go ahead and remove the old wiring now by removing each terminal from the junction box.Cut any excess wiring from your new cable and strip the wires of insulation using a crimper. Next, crimp ring terminals onto the new wiring. Place the terminals onto their corresponding studs in the junction box (ground wire to ground wire, brake wire to brake wire, etc). When finished, reinstall the nuts.Secure any excess wire with wire clips.
Trailer Junction Box - Remove Wiring
Trailer Junction Box - Strip Wire Insulation
Trailer Junction Box
Trailer Junction Box Wired
WITHOUT JUNCTION BOXIf you're not using a junction box and are simply connecting the new 7-way to your existing wiring, you can use butt connectors and a heat gun to make your wiring connections.Secure any excess wire with wire clips.
Butt Connector Trailer Wires

Vehicle Side

Now that our trailer is hooked up, it's time to wire our vehicle. Let's get started:
Step 1: Prepare for Vehicle Wiring InstallationIF YOU HAVE A 7-WAY CONNECTORIf your vehicle already has a 7-way connector, then great! Simply plug the trailer-end connector into the vehicle-end connector, and you're ready to roll.IF YOU HAVE A 4-WAY CONNECTORIf your vehicle has a 4-way connector, the easiest way to add a 7-way is with an adapter kit like the ETBC7, which includes everything you need to convert your 4-way into a 7-way. Confirm the function of your vehicle wires with a circuit tester prior to connecting. Activate each function (turn signal, brake lights, etc.) in turn and check for a corresponding signal from the circuit tester to make sure you have the right wire.IF YOU HAVE NO CONNECTORIf your vehicle lacks any kind of connector, the easiest way to install a 7-way plug is to install a 4-way and use an adapter. For help installing a 4-way connector, view our how-to guide here.Also take the time to confirm the function of your vehicle wires if you are splicing or clamping wires together. Check your vehicle's owner manual or use a circuit tester to confirm each wire's function prior to connecting. You can usually tap into your vehicle's wiring system with a circuit tester at the rear of the vehicle, behind the taillights. Activate each function (turn signal, brake lights, etc.) in turn and check for a corresponding signal from the circuit tester to make sure you have the right wire.
4-way to 7-way adapter
If you have a 4-way plug, add a 7-way with a 4-to-7-way adapter
Circuit Tester in Use on Trailer
Use a circuit tester to confirm wire function
Step 2: Make Vehicle ConnectionsYour wiring harness will either plug into, clamp onto, or splice into your vehicle's existing lighting. The type of connection depends on what is available for your vehicle model. We'll go over each process in more detail below.Some general notes and tips:
  • If the vehicle connector is under the vehicle, use a mounting bracket to attach it to the vehicle. This will help prevent damage that may occur if the connector is left dangling.
  • Use a small amount of grease on all electrical connections—the plugs on your automobile and the connector itself—to help prevent corrosion.
4-WAY TO 7-WAY ADAPTERSAn adapter will plug into your existing 4-way plug and provide two additional pins for your trailer brakes and battery lead. We've put together adapter kit # ETBC7, which includes everything you need to install a 7-way adapter, including the connectors, wiring, and circuit breakers.Once you plug the adapter into your existing 4-way, you will have an additional three wires that must be connected.One of these wires (typically blue but sometimes black) will run to your electric brake control power output. Another wire (typically black or red) will run to the positive terminal of the battery via additional wire and butt connectors.Use a circuit tester to test for wire function before connecting.
How to Wire Electric Trailer Brakes Diagram SAE
How to Wire Electric Trailer Brakes Diagram RV Standard
Watch video installation of 4-way to 7-way adapter installation
PLUG-IN STYLESome vehicle manufacturers essentially "pre-wire" your vehicle so that your wires are easily accessible for connection. T-connectors such as this one simply plug into your vehicle's existing wiring, no cutting or splicing required.The plug-in location is typically near the taillights, underneath the vehicle, or behind the paneling in the back cargo area. You may have to remove your trim access cover, scuff panels, taillights, etc. in order to access the plug.
Watch video installation of T-connector
SPLICE-IN STYLEHardwire kits aren't quite as convenient as the other styles, but splicing into your vehicle wiring is actually less difficult (and scary) than it sounds.After confirming your wire functions (using your owner's manual or circuit tester), connect your wires using one of three methods.Soldering: This is the best way to connect wires. Simpy solder your wires together for the strongest, most reliable connection using a soldering gun. Use heat shrink tubing to protect the soldered connection.Butt Connectors: If you aren't comfortable soldering wires, heat shrink butt connectors and a heat gun are the next best thing.Quick Splices: The quickest, easiest way to connect wires is by using a quick splice. Quick splices force a metal piece into two separate wires, thus connecting the circuit. NOTE: Quick splices are the easiest—but least reliable—wire connection method.
Trailer T-Connector
When FinishedAfter wiring up your trailer and vehicle, it's a good idea to plug the two ends together and test the function of each wire. Make adjustments as needed. If everything lights up when it's supposed to, you're good to go!
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Questions and Comments about this Article

Phil V.

I have a 2020 Ford F150 Raptor. When I connect my RV to the 7 pin plug it does not charge the battery on the RV. RV service center says it's the truck, Ford says it's the RV. Any idea who's right and or how do I get it to work ? When I had a Ford F250 super duty everything worked the way it's supposed too.

Etrailer Expert
Reply from Jon G.

Have you been able to test the truck and trailer separately from each other? If you have another truck and trailer with a battery (or a friend that would be willing to help out) then I would start there. It's also good to note that the 12V power pin on a 7-Way is only good for a maintenance charge really. It might be able to charge the battery some but it will be at a very low rate. If you're wanting to get a good charge on your RV battery while towing then I recommend going with one of the Redarc chargers because they do a great job at charging and maintaining batteries, plus they give you the option to tie in a solar panel setup if that's something on your radar as a future upgrade.

Reply from Phil V.

@JonG Thanks for the quick reply. I have an ultra tow electric jack that worked with my F250 but it won’t work with the F150. It has to be an issue with the F150 itself. Thoughts?

Etrailer Expert
Reply from Jon G.

@PhilV Is the jack equipped with a 7-Way that you are plugging in only for power? If it is only trying to pull power from the 12V pin then that's probably your truck. A lot of newer trucks are having this issue where they will only supply power to all 7 pins when they sense that a trailer is connected via the light functions.

Reply from Phil V.

@JonG I have an ultra tow electric jack that worked on my F250 when plugged into the trucks 7 pin but does not work on my F150 raptors 7 pin. Any idea why ?

Etrailer Expert
Reply from Jon G.

@PhilV If your jack only has wiring for the 12V power then your Ford pickup won't sense that a "trailer is connected" so it won't activate that power pin. What you'll need to do is tie the power for your jack into your trailer 7-Way wiring. You can do this a bit easier by using a junction box # e99009 .

Reply from Phil V.

@JonG Thanks. That’s exactly what’s happening. Ridiculous for what a truck costs today and it can’t do what older trucks can.

Etrailer Expert
Reply from Jon G.

@PhilV Yeah a lot of people are upset about it and rightfully so. I don't know the reasoning behind the change but I'm guessing it's maybe their attempt to try to keep the OEM wiring safe from corrosion or something along those lines.

Matt P.

Does the chassis of a utility trailer have to be connected to the vehicle ground for safety or any other requirements? The ground wires of all my trailer's lights are wired directly to the junction box connected to the 7-way plug, so a path through the frame is not electrically necessary.

Etrailer Expert
Reply from Jon G.

The ground wire on your vehicle 7-Way side should be attached to a bare metal surface on your vehicle while the ground wire on your trailer 7-Way side should be attached to a bare metal surface on your trailer. It is possible that the ground on your vehicle side is good enough for nothing to be grounded on your trailer-side of things but that's not the correct way to route your wiring.

Thomas L.

The black battery wire should be same size as the white ground wire - 10 gauge in chart - faq311-7-way-trailer-diagram-rv_2_800 The picture below this chart shows correct wiring for RV plugs. As a professional RV transporter I have seen to many trucks wired with those 2 wires to small and cause a fire from overheating. I built my own wire harness and none of the RV wiring was connected to the factory wire harness except the battery and brakes. My harness uses relays and 30 A circuit breakers. No problems since 1998 with my RV harness.

Etrailer Expert
Reply from Jon G.

You can use 10 gauge wire if you'd like but the standard is 12 gauge which is why we go that route - even your trailer brakes will likely have a 12 gauge ground wire. Adding extra protection with relays and circuit breakers isn't a bad idea either. We usually see those on the vehicle end though.

Thomas L.

7-Way Trailer Wiring Color Code RV Standard You have an error on this chart. The RED is left turn not a 12 v battery wire Anyone who wires their RV 7 blade plug according your chart will suffer so problems with no left turn or left stop light. the rest of the connections are RV standard connection with Yellow being optional.

Etrailer Expert
Reply from Jon G.

If you check out the 2 diagrams we have at the start of the article you can see that the Traditional SAE photo shows red being the power but the RV Standard photo shows red being the left turn/stop. Keep in mind that it's always a good idea to test for function before making any connections if you aren't sure what you have. While these are standard wire colors, we have seen them vary from time to time so doing a little bit of testing gives you a safety net to fall back on.

Reply from Cal

@JonG You defiantly have some errors in your RV standard color coded bar chart. Looks like someone mixed up some sae and RV standard designations. Look at the left column and the terminations on the right. Also 2 aux power colors and no left turn designation. You have a yellow reverse light wire being run to the left turn signal on the vehicle and terminating on the left turn signal bulb on the trailer.

Etrailer Expert
Reply from Jon G.

@Cal These colors can vary per RV and per vehicle so it's always a good idea to double check the function of each wire prior to making any connections.

Reply from Cal

@JonG I know the difference but someone else may not. One chart is correct but one of them is not. The incorrect chart conforms to no standard in the industry obviously.

Rick M.

I'm wireing a semi trailer and have three tail lights per side,the lights are marked ground/tail/stop,turn. White is ground brown is tail green is right turn,I have a red wire for brake but if hooked up to turn/stop wire it works but not together so what is wrong. Another words turn the blinker on fine but hit the brake it canceled the turn

Etrailer Expert
Reply from Jon G.

If you have a dedicated wire for a brake signal then you'll want to make sure it's connected to a brake-only circuit. If you're connecting that red wire to your green wire then that would explain why your lights aren't working correctly.

John B.

I have a travel trailer and the rear lights have only one bulb. I would like to replace with a two bulb light so that I can have back-up lighting. Is this possible or is my travel trailer not wired for backup lights? I have a 7-way connector from my pickup truck to the camper.

Etrailer Expert
Reply from Jon G.

You definitely can upgrade your trailer to include backup lights. It's really just a matter of routing the wire from your trailer 7-Way back to where you will install your new two bulb light and then making your connections. Usually the center pin of a 7-Way plug will carry the reverse light function so you do want to make sure your pickup has that pin active.

Reply from John B.

Thanks JonG. I'll check to make sure that center pin has juice when I put the truck in reverse.

Etrailer Expert
Reply from Jon G.

@JohnB No problem! Here is a link to our selection of lights and wiring if you don't already have that equipment.

Charlie C.

Thanks for the quick response. I was also directed to have another vehicle with a 7 way connector try to provide power to the camera. I used a 2007 GMC truck with towing package that also didn’t work.

Etrailer Expert
Reply from Jon G.

I'm guessing that the power wire for the camera is hot when you have your headlights on?

Reply from Charlie C.

After reading customer comments on the Furrion adapter I ordered one from etrailer, will have an answer in a few days. Thanks for the responses.

Etrailer Expert
Reply from Jon G.

@CharlieC No problem!

Reply from Charlie C.

@JonG Purchased adapter cable still no joy. Took RV to dealership were it was found to be faulty wiring during assembly at factory. Wire lugs were replaced and camera works great without adapter.

Etrailer Expert
Reply from Jon G.

@CharlieC I'm glad you were able to get it figured out! Happy camping!

Charlie C.

I have a Ford F 250 with towing package. I recently purchased a 2020 Dutchmen Kodiak Camper that has a built in wiring harness for a rear view camera (Furrion). Simple installation but can't get power to camera, called Furrion Tech Support and was told camera only gets power when headlights are on in manual. Tried, didn't work. Then informed that some car manufactures have current limitations on newer vehicles and that I can buy an adapter cord to solve the problem. Doesn't sound right?

Etrailer Expert
Reply from Jon G.

It is a little obnoxious but this is definitely a known problem. It's hard to pin down what specific vehicles this happens on which is why Furrion created their adapter # FR74FR to help remedy this when it pops up.

Keith

I have an enclosed trailer with great 12 volt DC interior LED lighting. It sits next to the garage and I do a lot of work in it. What’s the best way to Connect 120 volt AC power to run the 12 volt lighting? Currently I just hook up the truck when I need to use it but this is getting old. Is there a way to run a converter to the 7 way plug on my trailer?

Etrailer Expert
Reply from Jon G.

In order to accomplish this you're going to need a converter like part # 34266167 and a battery. The battery will send the power to the lights while the converter actually changes the power from AC to DC so it works with your lights. Then you can simply run an extension cord to make sure the battery is charged. If you only need the lights for a minute you won't have to hook anything up.

Reply from Keith

@JonG Thank you for the response. I will give this a try.

Ross T.

I have a 2002 Chevy Silverado 3500 at my company. Its got a trailer attached to it, but doesn't work. I've been trying to fix it and I notice that its wired wrong(7 wire harness). Also, there's an auxiliary battery near the trailer neck which is connected to the junction box ( meaning two wires from the truck harness itself aren't connected to the junction box). All the wires from the trailer are connected to the junction box. Is this auxiliary battery necessary?

Etrailer Expert
Reply from Jon G.

If it's a smaller battery and the trailer has electric brakes then that would be your breakaway battery box. It is necessary because it applies the brakes on your trailer in the event that the trailer becomes uncoupled.

Dord

Hi there, For people that already have a 4-way connector (e.g. by using Curt 55370) how would they go converting that to use 7-way connector and in particular something like Hopkins HM11141144? BTW HM11141144 is the best connector I saw with OEM like quality. I got that the +12V and ground for HM11141144 will come from the battery. Also the backup trailer lights will come from the car backup lights. I see how all the other trailer lights will come from 55370. What is not clear is what should be done with the trailer ground wire on the 4-way connector out of 55370. It cannot be used for trailer ground because it cannot carry enough Amps (55370 it's protected by a relatively small fuse). For trailer ground I already got the 10 awg wire from battery. Should I just ground that wire? Thanks

Etrailer Expert
Reply from Chris R.

Since you already have a 4-Way installed, and have your eyes on a 7-Way connector, all that you need is the Wiring Kit # 5506 . This includes the wiring needed to activate the new circuits on the 7-Way (brake output and 12V). The existing ground for the 4-Way will remain where it is.

Kevin

I have a 2013 Chevy Pickup 4-wheel drive. I hooked my trailer brake controller. It was working fine. Then I tapped into the power wire going to the controller, to power an emergency light. Just recently I reworked the wire connection and shorted out the power wire. Now I do not have power to the controller and no power at the two terminals at the front of the fuse box under the hood. The fuses look good at the front of the fuse box. Would anyone have an idea what the issue is.

Etrailer Expert
Reply from Chris R.

I have to imagine you popped the 12V brake controller fuse. I know you mentioned checking this, but it's all I can think of that would cause this. Check your Silverado's owner's manual to ensure you're looking at the right fuse location for that circuit. I also don't recommend tapping into that wire for anything else.

Reply from Kevin

@ChrisR Chris. I apologize for my error. I have check the fuse a couple of times. But not with a meter. I finally checked the circuit with multi- meter and replaced the fuses and the system works. I could not see where the fuse was bad. Thanks for your time and comments. Kevin

Etrailer Expert
Reply from Chris R.

@Kevin Awesome! I'm glad you were able to get it fixed.

Doru

I saw both 20A and 30A specified for the +12V Red wire with the mention that 20A will only be good for 2 and 4 brake magnets. My car towing weight capacity is max 3000lb and 200lb tongue weight - small, so the campers I'm looking at are small. So 2-4 magnets will be enough braking for me. Is there a way to find out how many magnets a trailer has? Is there a rule of thumb like one wheel one magnet?

Etrailer Expert
Reply from Chris R.

Each brake assembly uses a magnet - so the amount of magnets is equal to the amount of wheels on the trailer (assuming all the axles are equipped with brakes).

Doru

I would like a clarification on the wiring. I have a car that has a hitch harness in the trunk (power directly from battery, turn RH, turn LH, brake light, tail lights, ground directly to car body). I do not want to install any brake controller in the car. I plan to use a wireless one like Curt C51180. So in this case do I need to hook anything up on the Blue wire (electrical brake controller power output)?

Etrailer Expert
Reply from Chris R.

The blue (brake output) wire isn't needed at all for the Curt Echo # C51180 . It sounds like you've already got the 12V circuit active, so you don't need to change anything with your existing setup. Just plug the Echo in, pair it to your smart phone, and you're ready to go.

Anonymous

Very nice article. I would suggest adding a note that for the section at the end Soldering: This is the best way to connect wires. Simpy solder your wires together for the strongest, most reliable connection using a soldering gun. Use heat shrink tubing to protect the soldered connection. that its always important to have the right length enough to give a good overlap of the insulation after soldering and size just a little larger than the insulation, for a tight fit of heat shrink tubing already on the wire prior to soldering them together!!! Its easy to solder first and then go Hmmm... now how do I get this tube over my wire?

Roy B.

I would like to know how to best replace 2012 jayco 266RKS PULL behind 2 axel brake wires at wheel hub that tire blowouts made into spaghetti.

Etrailer Expert
Reply from Jacob H.

You can use 12 or 16 gauge wire to make this repair. We sell each of them by the foot I will provide a link for both.



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