Ford Wiring Fault On Trailer Message – What Does It Mean?

Because of the added vehicle strain and potential hazards that towing presents, Ford designed many notifications to pop up and inform its truck and SUV drivers about any trailer-related problems. One such warning is the "Wiring Fault On Trailer" message. So what does this notification mean? Here's what our research has uncovered.

Ford's "Wiring Fault On Trailer" message notifies the driver that there is an electrical problem with the trailer brakes. The problem can come from one of two sections of the trailer wiring connections:

  1. From the integrated trailer brake controller to the 7-pin connector (within the Ford vehicle), or
  2. From the 7-pin connector to the trailer brakes themselves.

When it comes to safe towing, we cannot overemphasize the importance of properly functioning trailer brakes. Do read on, because we've prepared some tips on how to find and solve this wiring fault problem on your Ford vehicle.

A parked Ford F250 truck, The F250 is a popular truck from Ford, this model happens to have a lift kit, custom wheels and a diesel engine. This model is also known as the King Ranch edition. - Ford Wiring Fault On Trailer Message - What Does It Mean?

What Does Trailer Wiring Fault Mean?

Whether you're pulling a small pop-up camper or a large travel trailer, towing a load behind your vehicle requires extra caution.

Although your truck or SUV may be powerful enough to pull that extra weight, you need the proper trailering equipment and driving prudence to conduct your trailering activity safely and confidently.

Coupling a truck with a trailer, pressure hoses, electrical wires

To keep its customers alert and informed about their trailering setup's conditions, Ford designed its vehicles to display several warning messages pointing to different types of trailer problems. One of these messages reads "Wiring Fault On Trailer."

Although the message appears to point to any trailer wiring in general, Ford explains that this warning specifically points to a short circuit on the electric trailer brake output line.

Because the fault message involves electric trailer brakes, we immediately know that we're talking about Ford vehicles equipped with the 7-pin (or 7-blade) trailer connector. All 4-pin trailer connectors, including those of Ford vehicles, only provide basic trailer lighting functions.

Ford also reminds us that this fault message can appear even when you don't have a trailer connected.

If the warning message appears while there is no connected trailer, then the notification should come with a single audible tone. This means that your wiring problem is somewhere from the integrated trailer brake controller on your dashboard up to the 7-pin connector near your rear bumper.

Alternatively, if the warning message only appears when you connect a trailer, then the problem is in your trailer's wiring—particularly in its electric trailer brake system.

The "Wiring Fault On Trailer" warning is very important and it needs your immediate attention. According to some Ford owners, this message often means that you may have already lost all trailer brake functions and you may be putting yourself and others on the road at risk.

What Should I Do If Wiring Fault On Trailer Message Appears?

repair electrics in the car, broken wires closeup

If the "Wiring Fault On Trailer" warning comes on while you're driving with no trailer connected, your biggest problem may just be the annoying message and sound. However, if the message appears right after you hook up a trailer, you should not attempt to drive out.

In the unfortunate event that the fault message appears while you're already towing a heavy trailer, we recommend that you pull over as soon as possible and call for roadside assistance. You may keep driving only if your trailer does not exceed the unbraked towing limit of the state and the manufacturer.

How Do You Diagnose Trailer Wiring Problems?

As with many electrical fault diagnoses, your first objective is to isolate the source of the problem. You can pinpoint the faulty wiring by testing the tow vehicle and the trailer separately.


If the "Wiring Fault On Trailer" warning appears while there is no actual trailer hooked up, then you should start testing the trailer circuit in your Ford vehicle. We recommend starting with the 7-pin connector itself as this component is the most exposed to the elements.

Check out this video on how a Ford F-150 owner solved his "Wiring Fault On Trailer" problem:

In many cases, dirt, moisture, and corrosion can accumulate in and around the 7-pin connector. These contaminants can cause a short circuit and trigger a wiring fault alert.

You may try to clean the 7-pin connector to see if it solves the problem. Applying some dielectric grease will help seal the electrical connection.

However, if you're dealing with an old trailer wiring harness, you may want to replace it altogether.

Check out this 7-pin trailer wiring harness for the 2015 to 2020 F-150s on Amazon.

Alternatively, the different wires of the trailer harness can chafe against each other and cause a short to power or short to ground. If you're comfortable working with automotive electricals, then you can isolate the problem using a handy multimeter.

Check out this best-selling multimeter on Amazon.


If the "Wiring Fault On Trailer" message appears right after you plug in your trailer's wiring harness to the 7-pin connector, then your problem lies with your trailer's wires. It's possible that one or more of your brake wires have a loose or shorted connection.

Ford also suggests that you check your trailer's emergency breakaway system. If the breakaway switch pin gets accidentally detached, the vehicle's trailer wiring system recognizes a short-to-voltage situation and displays a "Wiring Fault On Trailer" message.

Finally, Ford also says that a warning message can appear if your trailer brakes draw too much current from the battery. You may try lowering the "Gain" setting on your trailer brake controller to see if it resolves the issue.

Check out this video on how to diagnose your own trailer brakes at home. Even if you do seek an automotive technician's help, the video will still help you understand how trailer brakes work and the emergency breakaway system works:

What Are Ford's Trailer Messages?

Aside from the "Wiring Fault On Trailer" message, Ford also has other notifications that can help to trailer enthusiasts identify and solve their problems more easily.

Trailer Connection Status

Ford senses whenever an appropriate trailer wiring harness plugs into its trailer connector. From the factory, your Ford uses either a 4-pin or a 7-pin connector. 7-pin connectors usually come standard with higher-end models and trims or as components of Ford's tow package.

  • Trailer Connected
  • Trailer Disconnected

Trailer Brake Status

Ford trailer brake system informs you regarding the trailer brake settings (gain) and status, especially when something is wrong. Again, we recommend that you pay close attention to these messages to ensure that you have a safe and enjoyable trailering experience.

  • Trailer Brake Gain, No Trailer Connected
  • Trailer Brake Module Fault
  • Trailer Brake Gain

Trailer Lighting Faults

Aside from a trailer brake circuit, your Ford also provides the necessary connections for the different lights you need on your trailer. These include your trailer stop light, reverse light, turn signals, and other auxiliary lights. Here are the alert messages that appear when one of them may be having problems.

  • Trailer Lighting Module Fault See Manual
  • Trailer Stop Lamps Fault Check Lamps
  • Trailer Left Turn Lamps Fault Check Lamps
  • Trailer Right Turn Lamps Fault Check Lamps
  • Trailer Park Lamps Fault Check Lamps

Other Important Trailer Messages

  • Trailer Sway Reduce Speed - Some Fords come with the Trailer Sway Control (TSC) feature to help correct your trailer set-up's momentum during unsteady driving conditions. However, Ford also alerts you to reduce your speed when its sensors detect some trailer sway while you're driving.
  • Trailer Battery Not Charging See Manual - Displays when your trailer's battery does not charge through the trailer connector. This is important because your trailer battery powers all the lights and appliances in your trailer when it is disconnected from the tow vehicle.

How Do Trailer Brakes Work?

Checking the brake discs of a modern car. Vehicle braking system.

Like other vehicle brakes, trailer brakes stop your trailer's wheels from spinning. They are important components, especially for heavy trailers because the tow vehicle's brakes may not be sufficient to slow down or stop the momentum of both the vehicle and the trailer in time.

There are two general types of trailer brakes today: surge brakes and electric brakes.

Surge brakes rely on the momentum of the trailer. When the tow vehicle brakes, the trailer's weight shifts forward and compresses a master brake cylinder on the trailer hitch. The compressed cylinder then forces brake fluid through the brake lines to apply the brakes on the trailer wheels.

Modern electric brakes, on the other hand, use sensors to activate automatically when the towing vehicle brakes. The trailer's braking strength depends on the gain setting that the driver sets on the trailer brake controller. You may apply the brakes manually using the control knobs or buttons.

How Much Weight Can I Tow Without Trailer Brakes?

woman's hand checks the fixation of the trailer closed hitch lock handle on the towing ball towbar of the car closeup, the safety of driving with a trailer on the road

Different U.S. states have different laws on unbraked trailer towing weight limits. Although most states allow drivers to tow unbraked trailers up to 3,000 pounds in gross trailer weight, some states have much lower or higher limits. To illustrate, New York only permits 1,000 pounds, while Alaska allows even 5,000 pounds.

Wrapping Up

According to Ford, the "Wiring Fault On Trailer" warning message usually appears when something is wrong with the trailer brake circuit. This can be a loose connection, a short circuit, or a faulty wiring harness problem either in the tow vehicle or in the trailer itself.

To pinpoint the source of the problem, test first if the warning message appears only when you connect the trailer wiring or even when there is no trailer hooked up to your Ford vehicle at all.

Thank you very much for reading. We hope we were able to guide you properly in resolving your Ford's "Wiring Fault On Trailer" notification.

For more interesting reads about Ford vehicle alerts and other automotive topics, you may also check out these great articles:

How To Get A New Ford F-150 Key

Ford Starting System Fault? Here’s What To Do

Ford F-150 Tire Pressure Sensor Fault – What To Do?

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One comment

  1. I would like to put a hitch light in my opening when I don’t have a trailer connected. However when I put a hitch light in it I keep getting a warning saying there is a trailer connected. Is there a way around this?

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