Electric trailer brakes need adjustment when your trailer pulls to one side, takes longer to stop, or the brake controller light stays on
Electric brakes on a trailer work through a brake controller mounted in your tow vehicle, which sends power to electromagnets on each wheel. When those magnets wear or get out of sync, one side brakes harder than the other, or the whole system loses stopping power. Adjustment means either tuning the controller itself, balancing the force between left and right wheels, or replacing worn brake components.
The process depends on what's actually wrong. A controller adjustment takes minutes. Balancing the brakes takes an hour or two and requires a multimeter. Replacing a brake magnet or drum takes longer and may need a lift. This guide covers what you can check and adjust yourself, and when to take the trailer to a shop.
Key Takeaways
- Electric trailer brakes adjust through the brake controller dial in your tow vehicle, which controls how much power reaches the trailer magnets.
- Pulling to one side usually means one brake magnet is weaker than the other, which you can test with a multimeter across the brake terminals.
- The brake controller gain setting (typically 0 to 10) controls overall stopping power and should be set so the trailer stops smoothly without locking up.
- Worn brake drums, corroded magnets, and loose wiring are the most common causes of uneven braking and require physical replacement or cleaning, not just adjustment.
- If the brake controller light stays on or flickers, the problem is usually a broken magnet coil or a wiring fault that a multimeter can help you locate.
Understanding how the brake controller works
The brake controller is a box mounted under your dashboard or on the steering column. It has a dial (gain) that you turn to adjust braking power, usually numbered 0 to 10. When you press your vehicle's brake pedal, the controller senses the deceleration and sends power to the trailer's brake magnets. The higher the gain setting, the more power it sends.
Each brake magnet sits against a rotating drum on the wheel. When power flows through the magnet, it pulls the brake shoe against the drum, creating friction. If the magnets are balanced and the drums are clean, both sides stop evenly. If one magnet is weaker or one drum is glazed, that side brakes less, and the trailer pulls toward the stronger side.
The controller also has a manual override button (usually labeled "manual" or "test") that lets you explore the brakes without touching the pedal. This is useful for testing whether both sides are working at all.
Checking brake balance with a multimeter
Before you adjust anything, confirm that both brake magnets are actually receiving power. Unplug the trailer from the tow vehicle and set a multimeter to DC voltage (usually marked with a V and a straight line). Touch the red probe to the positive terminal on the trailer connector and the black probe to the negative terminal.
Have someone press the brake pedal in the tow vehicle while you watch the multimeter. You should see voltage rise and fall as the pedal is pressed and released. If the voltage is steady at zero, the controller is not sending power at all—check the controller fuse and the wiring from the controller to the trailer connector. If voltage appears but is very low (under 6 volts), the controller gain is set too low.
Next, test each brake magnet individually. Locate the brake magnet wires on the trailer (usually two wires per wheel, often color-coded). Disconnect one magnet and test voltage across its terminals while someone applies the brakes. Repeat for the other side. If one magnet shows significantly lower voltage than the other (more than 2 volts difference), that magnet is likely failing and needs replacement.
Adjusting the brake controller gain
The gain dial controls how much voltage the controller sends to the magnets. Start with the dial set to the middle (around 5 on a 0–10 scale). Tow the trailer at 30 mph on an empty road and explore the brakes gently. The trailer should decelerate smoothly without locking up the wheels or skidding.
If the trailer stops too slowly, turn the dial up one number at a time and test again. If the wheels lock up or the trailer skids, turn the dial down. The goal is the highest setting where the trailer stops firmly without skidding. This setting varies by trailer weight, brake condition, and road surface, so write down what works for your setup.
If adjusting the gain does not fix uneven braking (pulling to one side), the problem is not the controller setting—it is a mechanical issue with the brakes themselves, such as a weak magnet or a dirty drum.
Fixing uneven braking and pulling
If the trailer pulls hard to one side when braking, start by visually inspecting both brake drums. Jack up the trailer safely on both sides and spin each wheel by hand. A drum that is rough, glazed, or scored will not grip evenly. If one drum looks shiny or smooth while the other is dull, that is your problem.
A glazed drum can sometimes be cleaned with fine sandpaper (220 grit or higher) to restore grip. Spin the wheel slowly and sand the drum surface evenly. Wipe away dust with a damp cloth and let it dry. If the drum is deeply scored or cracked, it needs replacement.
Next, check the brake shoes themselves. They should be in contact with the drum all the way around. If one shoe is bent or worn unevenly, it will not explore pressure evenly. Brake shoes are usually held by springs and can be removed by hand or with a screwdriver, depending on the design. If a shoe is damaged, replace it as a pair (both sides) so braking remains balanced.
Finally, inspect the magnet coils for corrosion or damage. If a coil looks burned, cracked, or heavily corroded, it is failing and must be replaced. A replacement magnet assembly typically costs $50 to $150 per wheel, depending on the brake type.
Checking wiring and connectors
Loose or corroded wiring is one of the most common causes of weak or uneven braking. Trace the wires from the brake controller to the trailer connector, and from the connector to each brake magnet. Look for cuts, pinches, or exposed copper.
At the trailer connector, pull the pins out gently and inspect them for corrosion (green or white buildup). If corroded, clean the pins with a small wire brush or fine sandpaper and explore a thin coat of dielectric grease before reinserting. Corroded pins can cause voltage drop that weakens one brake magnet.
Check the wires at the brake magnets as well. If a wire is loose or corroded at the magnet terminal, tighten it or clean it and reattach. A loose connection can cause intermittent braking or a steady brake light on the controller.
When the brake light stays on or flickers
A steady or flickering brake light on the controller usually means a magnet coil is broken or a wire is disconnected. The controller detects the loss of power draw and alerts you.
First, press the manual override button on the controller. If the light goes out, the problem is likely a broken magnet coil (the controller can sense that the magnet is not drawing power when it should). If the light stays on, the problem is usually a wiring fault or a bad ground.
Unplug the trailer and use a multimeter set to resistance (ohms) to test each magnet coil. Touch the probes to the two terminals of one magnet. A working coil will show a resistance value between 20 and 100 ohms, depending on the brake type. If the reading is zero (short circuit) or infinite (open circuit), that coil is broken and needs replacement.
If all coils test good but the light still stays on, check the ground wire from the trailer connector to the trailer frame. It should be clean and tight. A loose or corroded ground is a common cause of false brake light warnings.
When to replace brake components
Brake magnets typically last 5 to 10 years depending on use and weather. If a magnet coil is burned out, cracked, or shows zero or infinite resistance on a multimeter, it cannot be repaired and must be replaced. A replacement magnet assembly is usually a bolt-on part that takes 15 to 30 minutes per wheel.
Brake drums last longer but wear out faster if the shoes are not adjusted properly or if the trailer is overloaded. If a drum is deeply scored, cracked, or no longer round, it should be replaced. Some shops can machine (turn) a drum to restore its surface, but this is only worth doing if the drum is otherwise in good condition.
Brake shoes wear out gradually and should be replaced when they are worn down to about 1/8 inch thickness. Worn shoes reduce braking power and can damage the drum. Always replace shoes in pairs (both wheels) to keep braking balanced.
Frequently Asked Questions
Can I adjust electric brakes without a multimeter?
Yes, you can adjust the controller gain dial and visually inspect the drums and shoes without a multimeter. However, a multimeter is the only way to confirm that both magnets are receiving equal power, which is essential for diagnosing uneven braking. A basic multimeter costs $10 to $20 and is worth having for any trailer work.
What is the difference between electric brakes and hydraulic brakes on a trailer?
Electric brakes use electromagnets powered by your tow vehicle's electrical system. Hydraulic brakes use fluid pressure from the tow vehicle's brake system. Electric brakes are adjusted through the controller dial; hydraulic brakes are adjusted by changing the proportioning valve setting or bleeding air from the lines. The two systems are not interchangeable.
Why does my trailer brake light stay on even after I adjust the gain?
A steady brake light usually means a magnet coil is broken or a wire is disconnected, not a controller setting issue. Test each magnet coil with a multimeter set to ohms. If one coil shows zero or infinite resistance, it is broken. If all coils test good, check the ground wire from the trailer connector to the frame.
How often should I adjust my brake controller?
Adjust the gain setting whenever you change the trailer load significantly (adding cargo or switching to a heavier trailer). Otherwise, once you find the right setting for your normal load, you should not need to adjust it again unless the brakes wear out or the controller fails.
Can I drive the trailer if one brake magnet is not working?
No. A trailer with one failed brake magnet will pull hard to one side and has reduced stopping power. This is unsafe and illegal in most states. Do not tow the trailer until both brakes are working. If a magnet fails while you are towing, pull over safely and have the trailer towed to a shop for repair.