How To Wire Electric Brakes On A Tandem Axle Trailer

Tandem axle trailers are safe and great trailer brands, which are rated to carry about 750kg to 2000kg and, by law, required weight brakes should have. However, any Tandem trailer carrying weight above 2000kg must have brakes on all axles. Notwithstanding, brakes are very vital to any vehicle’s safety.

Although wiring electric brakes can be complex, you can do it with little or no hassle. Before you begin wiring your Tandem axle trailer, it is essential to check for the type of wire plug your vehicle has. Knowing the plug type will make your wiring successful.

However, this article will help provide answers to these specific queries ranging from; how to wire electric trailer brakes on Toyota, does it matter which wire goes where on electric brakes, how you hook up electric brakes on a trailer, does it matter which wire is positive on the trailer brakes, how many wires do you need for electric brakes on a trailer, and more.

How do you hook up electric brakes on a trailer


Let’s get started right away!

How To Wire Electric Brakes On A Tandem Axle Trailer?

Installing electric brakes on your tandem axle trailer can seem daunting, but with the right instructions, it’s quite easy! Here’s how to get started:

Suppose your trailer has 7-way wiring that runs to the brakes, then, you may need to tap into the existing wiring system.

So you have to ensure that each of your new brakes has two wires for the brake magnet. One wire for 12-volt, which powers the brake magnets. The other wire is grounded either to the trailer frame or the primary trailer ground wire.

However, if the trailer wiring runs down the left side of your trailer, then slice the left side brake assemblies into the main electric brake power wiring from your 7-way connector. Similarly, run the jumper wire from the electric brake power wire to the right side of the brake assemblies. 

I recommend you use the 12-gauge wire, #12-1-1, for the jumper and additional ground wires. You could also use a duplex wire, but it should be a #10-2-1 wire. Or you follow the step below:

Steps to Wire Electric Brakes On A Tandem Axle Trailer:

  • You have to first look at the wiring harness for your electric brakes, which is usually located near the axles or hitch.
  • Next, find the Tandem Axle brake wires and the ground wire. Usually, the brake wire is blue or red, and the ground wire is usually white or green.
  • Now,  connect the brake wire to your brake controller by attaching it to the “output” terminal.
  • Having done that, you must now connect the ground wire to your vehicle’s clean, unpainted metal surface using a screw or clip.
  • Test your electric brakes to make sure they’re working properly.
  • Remember always to follow the instructions provided by the brake controller manufacturer, consult the owner’s manual of your trailer before starting the installation, and if you are not comfortable doing it yourself, don’t hesitate to hire a professional mechanic to help you out.”

How To Wire Electric Trailer Brakes On Toyota?

Here are the steps to wire electric trailer brakes on Toyota (Hilux);

  • Disconnect the negative battery of your vehicle.
  • Locate the vehicle’s main harness grommet. Cut off the tip of one of the nipples of the grommet.
  • Put the electric brake controller wires through the nipple hole into the vehicle’s cabin. Then put the input harness down through to the chassis undercarriage.
  • Beneath the vehicle, locate the power input harness.
  • Fix the power and ground input harness into the mating connector.
  • Locate the electric brake controller wires that are inside the cabin.
  • Mount the electric brake controller on the mounting bracket.
  • Connect the body harness connector to the electric brake controller.
  • Route the body harness towards the RHS of the chassis rail to the rear of your vehicle. Ensure it doesn’t come in contact with any moving parts.
  • Locate the trailer harness. Then, disconnect the trailer harness connector and the tail harness mating connector.
  • Patch in the body harness mating connectors. Then, connect the body harness (white wire) to the negative battery terminal.
  • Use a multimeter to test the body harness as you secure all harnesses.
  • Replace all removed parts and fasten all securely.

Sample Dual Axle Trailer Brake Wiring Diagram

Check out the wiring diagram of the dual axle trailer below;

dual axle trailer brake wiring diagram

Does It Matter Which Wire Goes Where On Electric Brakes?

Of course, not! In an electric brake, wires could go anywhere. Hence, the wires are not polarized, so you can run two conductor wires into your brake as you hook them on your trailer’s brake.

How Do You Hook Up Electric Brakes On A Trailer?

Hooking up electric brakes on your trailer is only possible with the brake controller. The first step is to install a brake controller, and the second is to hook it up to your trailer.

Check out the procedures to hook up electric brakes below;

  • Grab handy tools such as; a 2-3 mm drill bit, an electric drill, a no. 2 Philips head driver, a marker pen, lubricant, and a brake controller kit.
  • Disconnect the negative cable of your battery,
  • Hold and mark the device in the desired position.
  • Install the mount kit with a drill bit.
  • Mount your controller on its kit using self-tapping screws to hold it firmly.
  • Fix the harness to the unit, turn the ignition on and check the system. If necessary, you could adjust it.
  • Mount the 7-pin trailer plug connector under the truck using a bracket.
  • Drop the inner plug harness through your vehicle’s bumper or underneath the carriage if necessary.
  • Securely center and square the exterior plug on the vehicle. 
  • Connect the plug to the trailer lead into the pre-wired adapter of the brake controller.
  • Reconnect the negative cable of your battery.
  • Test and check if the system is functional.

Simple isn’t. Read on to learn more!

Does It Matter Which Wire Is Positive On Trailer Brakes?

It doesn’t matter which wire is positive on your trailer brake wiring. Additionally, you can use either wire as a positive wire. To this, as long as the current flows through the magnet in either direction. The trailer brake magnet would function properly.

How Many Wires Do You Need For Electric Brakes On A Trailer?

The number of wires you use for your electric brakes depends on the wiring system. If it is a 7-wire plug, you need two wires for your electric brakes. Precisely, one wire for power and the other for the ground. On the other hand, for a 4-wire system, you would need no wire for the electric brakes, only the brake light lights.

Tandem Axle Trailer Wiring Diagram

Here you have the wiring diagram of the Tandem axle trailer;

Trailer Brake Wire Gauge

There is always a range of wire gauges for trailer brakes and circuits. Although, when comparing the thickness of your wire, a smaller gauge could mean a thicker wire. However, the National Electrical Code has a generally accepted rating of; 14-gauge wire for an allowable ampacity of 20 amps of current at an ambient temperature of 30 degrees. 

Similarly, if you use a standard minimum of 16-gauge wire in your trailer brake, you have an allowable ampacity of 15 amps or 16 amps at maximum brake load.


Finally, a typical Tandem axle brake wiring is color coded. However, the trailer’s brake circuit is usually blue wire moving to the brake magnet’s power wire. The brake magnet has power and ground wires, although the ground wire is attached to the vehicle’s frame. Check for more details on the brake magnet from the diagrams above.

Wiring your electric brake on a Tandem axle trailer could be effortless if you have basic knowledge of RV and SAE wiring standards. Perchance, I have outlined the steps of hooking up your trailer in the above guide. Always use your owner’s recommended wiring system, and seek assistance from a technician when necessary. Do well to share this post with others!

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