How to test trailer electric brakes - all you need to know
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As a trailer owner, you understand the importance of brakes. Electric brakes are standard on medium duty trailers.
Trailer electric brakes are often tested by first looking at the brake controller. If your brake controller is OK, check for wiring problems and short circuits inside the brake magnets themselves.
You need reliable brakes for pulling heavy loads or going up and down dangerous mountain roads. You should not take your car out onto the road if you have reason to believe that the brakes are not working properly, so if you notice a problem, fix it as soon as possible.
How to test trailer electric brakes
Now let's look at your electronic brake control panel. If you have a model with a screen, you will know if there is a problem if the screen lights up.
The electric brake controller on a trailer is a device that supplies power to the electric brakes. When you step on the brake pedal of your tractor, the electromagnets inside the brakes turn on and your trailer comes to a stop.
The magnetic action of the brake controller can be checked in the following ways:
1. Compass Test
Simple, primitive, but useful! I don't know if you have a compass handy, but here's a simple test to see if you do.
Use the controller to apply the brakes (you may need a friend to help you with this) and place the compass next to the brake. If the compass doesn't turn, your brakes aren't getting the power they need to work.
You should check the wires and connections for damage if the test fails and the compass does not spin. Although this test is quite entertaining, few people have a compass these days; so if you have a screwdriver or wrench handy, we have a test that's even easier for you!
2. Wrench test
When the electromagnetic field is turned on, metal objects should stick to it. If your wrench (or other metal object) is holding well or poorly, you can also tell how much force you are applying.
When you use the controller to apply the brakes, they work well as long as your wrench sticks to them. If not, you need to recheck the connections and wiring.
Using the BrakeForce Meter
An electric brake force meter is another tool that can be used. It can simulate your load and tell you how your trailer should react when you step on the brake pedal.
Checking the brake system with a trailer connected
If everything is fine with the brake controller, but the brakes still do not work, the problem may be in the wiring or connections. A multimeter can check the connection between the brakes and the brake controller.
To figure out how much power your brakes need, you need to know how big they are and how many there are. Most trailers have at least two brakes (one for each axle). If you have more than one axle make sure you add the correct amount of brakes.
For this test, you will need a fully charged 12-volt battery and knowledge of how to set up a basic 7-pin trailer plug:
Connect the blue brake control wire to the ammeter on the multimeter between the brake controller and the trailer connector. It would be helpful if you tried to get the maximum:
Brake diameter 10-12″
7.5-8.2 amps with 2 brakes
15.0-16.3A with 4 brakes
Using 22.6-24.5 amps with 6 brakes.
Brake diameter 7″
6.3-6.8 amps with 2 brakes
12.6-13.7A with 4 brakes
Using 19.0-20.6 amps with 6 brakes.
If your reading is higher (or lower) than the numbers above, you should test each brake to make sure it's not broken. Make sure your trailer is NOT connected this time:
- Test 1: Connect the ammeter setting of the multimeter to the positive lead of the 12 volt battery and either of the brake magnet leads. It doesn't matter which one you choose. The negative end of the battery must be connected to the second magnetic wire. Replace the brake magnet if the reading is 3.2 to 4.0 amps for 10-12" or 3.0 to 3.2 amps for 7" brake magnets.
- Test 2: Place the negative lead of your multimeter between any of the brake magnet wires and the positive battery terminal. If the multimeter reads ANY amount of current when you touch the negative battery pole to the base of the brake magnet, your brake has an internal short circuit. In this case, the brake magnet must also be replaced.
How to test trailer brakes with a multimeter
Set the multimeter to ohms to test the trailer brakes; Put the negative probe on one of the brake magnet wires and the positive probe on the other magnet wire. If the multimeter gives a reading that is either below or above the specified resistance range for the brake magnet size, then the brake is defective and needs to be replaced.
This is just one way to test every brake.
There are three ways to check that something is wrong with the brakes:
- Checking resistance between brake wires
- Checking the current from the brake magnet
- Control current from electric brake controller
F.A.Q.
1. How do I know if my trailer's brake controller is working?
During a test drive, depressing the pedal doesn't always tell you which trailer brakes are working (if at all). Instead, you should be looking for a bar that slides over your brake controller. It will include either an indicator light or a numeric scale from 0 to 10.
2. Can the trailer brake controller be tested without a trailer?
Absolutely! You can test your trailer's electric brakes without connecting it to the tractor using a separate 12V car/truck battery.
3. Can I test battery trailer brakes?
Trailer electric drum brakes can be tested by directly connecting +12V power from a fully charged battery. Connect power to the hot and ground terminals on the trailer or to the two wires of the independent brake assembly.
Summing up
There are many ways to find out why the brakes on a trailer aren't working. We hope this guide has been helpful to you.
