When you’re getting your vehicle set up for towing, the towbar creates the physical connection to the trailer, boat, caravan or whatever you are towing. That’s only part of the story, though – you also need an electrical connection.
That’s where a towbar wiring harness comes in.
The wiring harness connects your vehicle’s electrical system to the trailer socket. It powers your trailer indicators and lights, as well as the electric brakes if your trailer has them installed.
In this article, we’re going to break down everything you need to know about a towbar wiring harness and why it’s an essential part of your towing setup.
What Is a Towbar Wiring Harness?
A towbar wiring harness is the set of cables, connectors, and components that connect your vehicle’s electrical system to the trailer socket. It plugs into the factory wiring loom on your vehicle, runs down the length of the car to the 7-pin or 12-pin trailer plug socket installed on the towbar.
Other terms you may hear that refer to the wiring harness include:
- Trailer wiring harnesses
- Towbar wiring kits
- Trailer wiring kits
- Towbar electrics
A distinction we need to make is that the towbar wiring harness is installed on your vehicle, while the trailer wiring harness is installed on the trailer, taking power from the plug socket to the lights and brakes.
What Does a Towbar Wiring Harness Do?
The towbar wiring harness carries electrical signals from your vehicle to your trailer or caravan.
It depends on your towing setup, but these can include:
- Indicators
- Brake lights
- Tail lights
- Electric trailer braking functions
- Auxiliary electrical functions
Auxiliary electrical functions would be things like an onboard trailer battery, caravan lighting or other 12 volt accessories on the trailer.
How Does the Electrical Connection Work?
The basic connection looks like this:
Vehicle electrical system → wiring harness → trailer socket → trailer
The wiring harness connects the vehicle’s electrical system to the trailer socket mounted near the towbar. Your trailer or caravan then plugs into this socket.
The socket itself may use a 7-pin, 12-pin or another configuration depending on the application.
We’ve covered those differences separately in our 7-Pin vs 12-Pin Trailer Plugs guide.
Does Every Towbar Need a Wiring Harness?
Not necessarily. Whether you need towbar wiring depends on how you’re going to use the towbar.
Towing a Trailer or Caravan
If you’re towing something that requires road lights or other electrical functions, you’ll need an appropriate electrical connection. If you’re towing a trailer with a GTM (Gross Trailer Mass) of over 750kg, trailer brakes are a legal requirement.
This applies to many:
- Box trailers
- Caravans
- Boat trailers
- Camper trailers
- Horse floats
Your exact wiring requirements will depend on what you’re towing and the equipment fitted to it.
Using a Towbar for Accessories
A towbar can also be used to carry accessories such as bike racks. You’re not hooking up to a conventional trailer, so you may not require the electrical connection. Chat to your towbar installation expert about what you’re going to be using the towbar for and they will guide you to the right electrical setup.
Are All Towbar Wiring Harnesses the Same?
No. Towbar wiring can differ considerably between vehicles.
Two broad categories you’ll encounter are universal wiring and vehicle-specific wiring.
Universal Towbar Wiring
Universal wiring kits are made for use across a range of vehicles rather than one particular make and model. Installation depends on the vehicle’s electrical system and the kit used.
Vehicle-Specific Towbar Wiring
Vehicle-specific wiring is made for a particular vehicle or range of vehicles. These kits can include connectors and electronic components intended to integrate with the vehicle’s existing electrical system.
Why Do Modern Vehicles Need Different Towbar Wiring?
Modern vehicles can have sophisticated electrical and computer systems. You need towbar wiring that works with the system, not against it. The following are all fairly standard features on modern vehicles now:
- Parking sensors
- Reversing cameras
- Stability control systems
- Driver-assistance systems
- Trailer detection
- Electronic control modules
They can all affect how towbar wiring needs to be installed. This is where a professional towbar installation becomes worthwhile. You don’t want to wing it on the electrics in a late-model vehicle.
The following features also come into play:
Trailer Detection
Some vehicles are able to recognise when a trailer has been connected. The vehicle may then adjust certain systems or functions while towing. For this to work correctly, the wiring needs to be compatible with the vehicle’s electrical system.
Electronic Modules
Some towbar wiring installations use an electronic module rather than connecting the trailer circuit directly to the vehicle’s lights.
Vehicle Coding
Certain vehicles may require coding after towbar wiring has been installed so the vehicle recognises the towing equipment correctly. This doesn’t apply to every vehicle, which makes it important that your towbar wiring is compatible with your vehicle.
What Happens If Towbar Wiring Is Incorrect?
When it comes to towing, safety is always the number one priority here at Speedy Towbars. If your wiring is incorrect, you get electrical problems, and electrical problems can be a significant safety concern.
Common symptoms of incorrect towbar wiring include:
- Trailer lights not working
- Brake lights or indicators operating incorrectly
- Intermittent trailer lights
- Blown fuses
- Dashboard warning lights
- Trailer detection problems
- Parking sensor issues
Faults can also develop over time. Due to factors including:
Loose Connections: A loose electrical connection can cause trailer lights to work intermittently or stop working altogether.
Water and Corrosion: Trailer sockets are exposed to the elements, so moisture and corrosion can affect electrical connections.
Incorrect Wiring: Connections made to the wrong circuit can cause lights to behave incorrectly and may create faults elsewhere in the vehicle.
Do Towbar Wiring Harnesses Include the Trailer Plug?
Yes, most trailer wiring harness kits include the trailer socket plug that attaches to the towbar at the rear of your vehicle. Standard core inclusions include:
- Trailer plug (7-pin)
- Wiring loom
- Connectors
Can You Install a Towbar Wiring Harness Yourself?
DIY towbar and wiring harness installations are a viable option if you know what you’re doing. We don’t recommend it if you’re a beginner, as the required adjustments can be complex depending on your vehicle and the wiring harness you’re using. These could include:
- Vehicle-specific wiring
- Electronic modules
- Integration with existing vehicle systems
- Vehicle coding
- Specialist diagnostic equipment
Before attempting a DIY installation, you need to know which wiring system is compatible with your vehicle and how to connect it. If your vehicle has advanced electronics or you’re not sure what you’re doing, a professional installation can reduce the risk of wiring faults and compatibility problems.
If you’re in Brisbane or surrounds, The Speedy team can take care of it for you. If you’re anywhere else in Australia, have a chat to your local mechanic or towbar installer and see if they can help out.
How Do You Choose the Right Towbar Wiring Harness?
Choose your wiring setup based on both your vehicle and what you’re towing.
Check Your Vehicle
The make, model, and year can determine which wiring kits are compatible and whether you need additional electronics.
Consider What You’re Towing
A basic trailer may have different electrical requirements from a caravan with electric brakes and auxiliary equipment.
Check Your Trailer Connection
You also need the correct socket for the trailer or caravan you’re connecting. In Australia, 7-pin and 12-pin connections are common. The appropriate option depends on the functions you need.
Check for Additional Electrical Requirements
Depending on your setup, you may also need equipment for electric brakes, auxiliary power or other towing functions.
Get the Right Towbar Wiring Harness for Your Vehicle
Towbar wiring isn’t a one-size-fits-all product. We stock a wide range of towbar wiring harnesses online, with nationwide shipping available. The correct harness will depend on your vehicle, its electrical system and what you plan to tow. Our friendly team is always available to help guide you to the right product.
Remember that if you’re in Brisbane or surrounds, our mobile towbar installers can come to your home or workplace for your towbar and wiring installs. You can also bring your vehicle into our Everton Hills or Slacks Creek workshops.
Any questions? Get in touch today!
Jordan is the co-owner of Speedy Towbars and a trusted source of towbar knowledge for Queensland drivers. When he's not installing towbars, he treasures time with his family and hitting the road for caravanning adventures!