Molly Ayala
Testing electric trailer brakes is a crucial safety measure before hitting the road. While specific testing procedures may vary depending on the trailer's make and model, some general testing methods can help diagnose potential issues. One common approach involves using a multimeter or ohmmeter to measure resistance and voltage. By setting the multimeter to Ohms and placing the probes on the brake magnet wires, you can determine if the resistance falls within the specified range for the brake magnet size. Additionally, applying voltage to the system and observing the brake's response can provide valuable insights. Other factors to consider include the number of brakes, trailer pin plug configuration, and recommended current for the magnet wires. Conducting these tests ensures safe and reliable trailer brake performance, allowing for peace of mind while towing.
Testing Electric Trailer Brakes
| Characteristics | Values |
|---|---|
| Tools | Multimeter/Ohmmeter, Voltmeter |
| Steps | 1. Set the multimeter to Ohms (Ω). 2. Place the negative probe on one of the brake magnet wires and the positive probe on the other. 3. Measure the resistance. 4. Compare the reading to the specified resistance range for your brake magnet size. |
| Expected Readings | For a 10-inch brake drum, expect a reading between 3.8 – 4.0 ohms. |
| Interpretation | If the reading is outside the expected range, the brake or magnet may be faulty and need replacing. |
| Additional Checks | 1. Measure the current with the car powered on and the brakes activated. 2. Jack up a wheel, apply voltage, and spin the wheel to see if the brake applies. |
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What You'll Learn
Using a multimeter to check for resistance
To test electric trailer brakes using a multimeter, you need to check for resistance. This is done by setting your multimeter to Ohms (Ω). Place the negative probe on one of the brake magnet wires and the positive probe on the other magnet wire. It doesn't matter which wire the black or red probe is placed on as there is no polarity between the brake magnet wires.
For a 10-inch brake drum, you should expect a reading between 3.8 and 4.0 ohms. If the reading falls outside this range, then the magnet is faulty and needs to be replaced. For instance, if the multimeter displays "O.L", it indicates a short in one of the wires, and the magnet will likely need changing.
You can also use an ohmmeter to measure the resistance at the main trailer plug-in cord. If you look at it from the end with the nub at the top, the trailer brake contact is at the 7 o'clock position. Take the resistance from that to a frame ground. If the resistance is 1 ohm, it means that each magnet has a resistance of 4 ohms, as they are wired in parallel.
Another way to test the brakes is to jack a wheel up, apply voltage, and spin the wheel to see if the brake applies. If it doesn't work, check that there is power to and a ground for the magnet before pulling the wheels.
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Testing the breakaway brake battery
The breakaway controller is designed to apply the electric brakes if your trailer accidentally disconnects from your vehicle. The breakaway battery is charged by the vehicle while towing. However, if the trailer becomes disconnected, the breakaway battery will power the trailer brakes. Therefore, it is crucial to test the breakaway battery every three months or as recommended by the manufacturer.
To test the breakaway brake battery, follow these steps:
- Ensure the trailer is hitched to the tow vehicle.
- Check the breakaway battery's state of charge; it should be fully charged.
- Unplug the trailer connector from the tow vehicle.
- Pull out the pin from the breakaway switch. This typically requires approximately 40 pounds of force.
- Try to pull the trailer with the tow vehicle. The trailer wheels will rotate slightly, applying the brakes.
- Observe if the trailer rolls freely. If it does, the breakaway system or trailer brakes may require servicing or adjustment.
- Reinsert the pin into the breakaway switch and reconnect the trailer plug to the tow vehicle.
Additionally, you can test the breakaway battery by pushing the test button on the unit. The indicator lights should illuminate, indicating that the unit is functioning correctly. When connected to the car battery and the caravan is plugged into a power source, ensure that the charging light indicates the breakaway battery is charging.
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Measuring the current with a probe
To test electric trailer brakes by measuring the current with a probe, you will need a multimeter or ohmmeter. The multimeter should be set to Ohms, which is usually represented by the Omega symbol (Ω). This will allow you to measure the resistance.
First, identify the brake magnet wires. One is the blue wire coming from your connector plug, and the other is one of the wires connected to your brake magnet. With your car powered on, activate the brakes through the pedal or electric control panel.
Now, connect the probes to the wires. It doesn't matter which probe goes where, as there is no polarity between the brake magnet wires. Place one probe on the blue wire and the other on one of the brake magnet wires.
At this point, you can measure the amount of current coming from the connector to the brake wires. Check the specifications for your trailer to determine the recommended current based on the size of the magnet. If the current goes above or below this specification, then the controller or wires may be faulty and need to be replaced.
For example, for a 10-inch brake drum, you should expect a reading between 3.8 and 4.0 ohms. If the reading is outside this range, the magnet is likely bad and needs to be replaced. Additionally, if the multimeter displays "O.L", it indicates a short in one of the wires, and the magnet probably needs to be changed.
You can also test the breakaway brake battery by removing the pull pin from the switch and attempting to pull the wheelhouse forward. The wheelhouse should resist being towed, indicating that the breakaway brakes are functioning correctly.
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Applying voltage to the jacked-up wheel
To test electric trailer brakes by applying voltage to a jacked-up wheel, follow these steps:
- Jack up the trailer: Use a jack to lift the trailer and securely support it, ensuring the wheel is off the ground and able to rotate freely.
- Connect the battery: Connect a 12-volt battery to the trailer brake magnets. Ensure the battery is fully charged before testing.
- Apply voltage: With the voltage applied directly to the brake magnets, you are simulating the emergency breakaway switch, which engages the brakes in the event of the trailer detaching from the towing vehicle.
- Spin the wheel: Once the voltage is applied, spin the jacked-up wheel briskly. Observe if the magnet is activated and the braking mechanism engages, causing the wheel to slow down or stop.
- Inspect for issues: If the brake does not engage, there may be issues with the ground connection or internal wiring. Check for loose connections, damaged wires, or rattling parts inside the drum.
- Compare resistance readings: Use a multimeter to measure the resistance at the main trailer plug. Compare this reading to the expected resistance range for your specific brake magnet size. If the reading is outside the specified range, the brake may need to be replaced.
Remember to exercise caution when working with electrical systems and ensure you have the necessary knowledge and equipment to perform the test safely.
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Checking for wiring issues
Firstly, it is important to understand the configuration of your trailer's electrical system. Note the number of brakes, the trailer pin plug configuration, and the recommended current for the magnet wires, which is based on the size of the magnet. This information will be useful as you test and diagnose any issues.
One common point of failure is the Scotch lock, especially in circuits under trailers or around taillight wiring. Scotch locks can cut wire strands if used on the wrong gauge wire and can also cause corrosion. Therefore, it is a good idea to inspect these components first.
To test the wiring, you can use a multimeter or an ohmmeter. Set your multimeter to Ohms (usually denoted by the Omega symbol, Ω). Place one probe on one of the brake magnet wires and the other probe on another magnet wire. If your trailer has a blue wire, you can connect one probe to it and the other probe to one of the brake magnet wires.
If your multimeter shows a reading outside the specified resistance range for your brake magnet size, there might be an issue with the wiring or the controller. For example, if you have a 10-inch brake drum, the reading should be between 3.8 and 4.0 ohms. If the reading is significantly different, the wires or controller may be faulty and need replacement.
Additionally, you can perform a simple test by jacking up a wheel, applying voltage, and spinning the wheel to observe if the brake engages. This test can help determine if the wiring and electrical system are functioning correctly.
Remember to consult a qualified professional or a dealer if you are unsure about any aspects of testing or repairing electric trailer brakes.
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Frequently asked questions
Before towing, you must test your trailer's electric brakes to ensure safety. Here are three methods to do so:
- Jack a wheel off the ground and rotate it briskly to see if the magnet is activated and the braking mechanism works.
- Use a multimeter to measure the resistance at the main trailer plug. If the resistance is within the specified range for your brake magnet size, the brakes are functioning.
- With your car turned on, activate the brakes and measure the current coming from the connector to the brake wires. If the current is within the recommended specification, the brakes are functioning.
The resistance range will depend on the size of your brake drum. For example, for a 10-inch brake drum, you should expect a reading between 3.8 and 4.0 ohms.
If your trailer brakes are not functioning, do not tow your trailer. Take your trailer to a qualified specialist to evaluate and repair the brake system.
