How to Troubleshoot a Malfunctioning Trailer Brake System

Introduction

When you’re towing heavy loads, safety depends on a fully functional trailer brake system. A malfunctioning brake system can lead to poor stopping power, trailer sway, or worse—an accident on the road. Fortunately, you don’t have to be a professional mechanic to troubleshoot your trailer brakes. With the right approach and some basic tools, you can identify common issues and take steps to correct them before they become costly problems.

In this guide, we’ll walk you through the essential steps to troubleshoot a malfunctioning trailer brake system, covering both mechanical and electrical aspects. Whether you’re experiencing weak braking, no response, or erratic performance, this article has you covered. Let’s dive in.

Start with a Visual Inspection

Before getting deep into diagnostics, begin with a thorough visual inspection. This simple step can reveal obvious issues that may be causing the malfunction.

What to look for:

• Check the trailer wiring harness for visible damage, corrosion, or loose connections.
• Examine the brake controller wiring inside the vehicle—especially the blue brake output wire.
• Look for signs of frayed insulation, pinched wires, or broken connectors on the brake magnets.
• Inspect the brake drums or rotors for rust, grooves, or debris buildup.
• Ensure the breakaway switch and battery are intact and functioning.

Many trailer brake problems are electrical in nature, and in such cases, damaged or improperly installed wiring is often the culprit. Using corrosion-resistant materials like copper-clad aluminum (CCA) wire helps ensure consistent brake signal transmission and durability over time.

Test the Trailer Brake Controller

The brake controller in your towing vehicle is the brain of the system. If it's not functioning correctly, your trailer brakes won't receive the proper signal. 

To test it:

• Make sure the controller powers on when you start the vehicle.
• Engage the manual override and watch the display (if digital). It should show a numeric output.
• Check if the trailer brake lights activate when pressing the vehicle’s brake pedal.
• Use a multimeter to test for voltage output on the blue wire at the trailer plug—there should be an increase in voltage as you apply braking force.

If the controller is not delivering the right signal, verify that the ground wire is securely connected and that the controller’s power supply is uninterrupted. Upgrading or replacing any worn wiring may restore stable performance.

Inspect the Trailer Brake Magnets

Trailer brake magnets are a common point of failure in electric brake systems. If they aren’t working correctly, your trailer brakes won’t respond.

To inspect:

• Raise the trailer using jack stands and remove the wheels.
• Examine the magnets for excessive wear or visible damage.
• Use an ohmmeter to check the resistance. Most brake magnets should read between 3.0 and 3.8 ohms (per magnet). If you get a reading outside this range, the magnet may be faulty.
• Spin the wheel and apply power to the magnet (carefully). You should feel the wheel resist motion if the magnet engages.

If one or more magnets are worn out, replacing them with compatible units is the best solution. Also, verify the wires going to the magnets—look for secure connections and consider replacing older wires with corrosion-resistant variants to improve longevity.

Check Grounding and Electrical Continuity

Trailer brake systems rely on a solid ground to function. A poor ground connection can disrupt the entire circuit, leading to weak or no braking.

Troubleshooting steps:

• Verify that all grounds (both vehicle and trailer) are clean, tight, and corrosion-free.
• Test continuity from the vehicle’s ground to the trailer’s ground using a multimeter.
• If you're getting inconsistent readings or resistance, clean all contact points and replace corroded or damaged wires.

Often overlooked, grounding is one of the most critical—and easiest to fix—issues in brake systems. Using CCA wire for both positive and ground paths can help maintain consistent conductivity, especially in harsh towing environments.

Confirm Brake Adjustment and Mechanical Operation

Sometimes the issue isn’t electrical—it’s mechanical. If the brake shoes are out of adjustment or worn down, they won’t contact the drum properly.

What to do:

• Remove the brake drum and inspect the brake shoes for wear.
• Use a brake adjustment tool to slightly expand the brake shoes so that they lightly contact the drum when reassembled.
• Rotate the wheel to check for slight drag. If there’s none, the brakes may be too loose.
• Apply and release the brake controller while listening for clicking or engaging sounds.

Regular brake adjustment is essential, especially on drum brakes that don’t self-adjust. This task should be part of your maintenance routine for safe and efficient braking.

Conclusion

Troubleshooting a trailer brake system might seem daunting, but with patience and the right steps, it’s totally manageable. Begin with visual checks, then move through the system methodically—controller, wiring, magnets, grounding, and mechanical parts.

Remember, the safety of your trailer and cargo—and everyone else on the road—depends on a reliable brake system. Keeping it in top condition ensures smoother trips and peace of mind every mile you travel. Get to know us better on our About Us page, or reach out directly with your questions. Let’s get your trailer powered up and ready for adventure!

For help with diagnostics and personalized wiring plans, try using our Expert Software Tool, which generates tailored instructions based on your trailer’s unique configuration.