Testing Electric Trailer Brake Magnets with a Multimeter

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Question:

lost brakes on my 38 foot goose neck trailer and cant seem to get them to work use to hear the brake magnets when i applied the brakes can i hook a 12 volt battery directly to the magnet wires to test them or is there a ohm reading or some other way of testing the electromagnets.

asked by: Robert A

0

Expert Reply:

The brake magnets can be tested in the manner you have suggested, just make sure that the trailer is not connected to the vehicle when performing this test. You would not want to short out the brake controller or worse. I would check the magnets for wear before going on to test them with a meter. If the magnets show abnormal wear or if you can see the windings beginning to show through the friction surface of the magnet then they will need to be replaced.

To test the Brake magnets with an ammeter,item # PT89ZR, you would connect the ammeter between the positive terminal of a battery and one of the magnet wires, then connect the other magnet wire to the negative battery terminal. Check the amperage, if the amperage is greater than the specified amount (see chart below), replace the magnet. If the reading is less than the specified amount, then the leads are bad and the magnet should be replaced.

Electromagnet Specifications

7 inch Diameter Brake Drum
Max Amps at 12-13 Volts
1 Magnet 3.0 - 3.2

10 and 12 Inch Brake Drums
Max Amps at 12-13 Volts
1 Magnet 3.2 - 4.0

Next disconnect the negative wire from the brake magnet wire and connect it to the base, housing, of the brake magnet. If there is any amperage the magnet is shorted and will need to be replaced.

Finally, using an ohmmeter check the resistance between the brake magnet wires. If the resistance is not within the the specified range (see below) then the magnet will need to be replaced.

7 inch brake magnet resistance should be 3.8-4.0 Ohms
10 and 12 inch brake magnets resistance should be 3.2-3.5 Ohms

expert reply by: Robert G

0

Answer 1

There are a number of reasons why the brakes on your trailer may not be working. Lets start with the easiest things to check. First, check the vehicle and trailer connectors for corrosion. This can cause a short inside the connector and the brake…

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Answer 2

Brake magnet wires like what are on the brake assembly #23-106 that you referenced can be wired up with either wire getting the positive and the other getting the ground. As long as current runs through them it doesn't matter which wire gets…

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Answer 3

There are many things that can affect the voltage on the brake output wire from your brake controller to your trailer brakes such as the power setting on your brake controller, how you are testing the wire and if you are testing it with the brakes or…

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Answer 4

To use the Curt Echo Wireless Trailer Brake Controller #C51180 your vehicle only needs 12 volt, ground, and turn signals connected to its 7-way socket. What this means is you do not need the brake signal from the 7-way. For example, if you used a…

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Answer 5

First, do a visual inspection. You should make sure that the front of the magnet is not worn to the point where the interior copper windings are visible. Also, check the armature surface (inside rear of brake drum where magnet rides) is free of…

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Answer 6

It should be getting close to 12 volts if the power output is set to the maximum on the brake controller. Some brake controllers will not work properly if they are titled or turned to the side or if it has a leveler knob that is not level. Check…

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Answer 7

This is a fairly common problem that is almost always due to corrosion on the trailer connectors. Check both the connector on the tow vehicle and on the trailer for corrosion and/or a bent pin and fix as needed. I attached a help article on…

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Answer 8

If your trailer has 7 wires running all the way back to the brakes, then yes, you can tap into the existing wiring. Each of your new brakes will have two wires for the brake magnet. One wire is for 12 volt power to the brake magnets and the other…

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Answer 9

BTR is a standard spindle that a lot of trailer axles have on them. It seems that your trailer has a BTR spindle which makes picking out a hub pretty easy. For an idler hub you would want the part #8-258-5UC1-EZ. Or if you want a brake drum you would…

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Answer 10

The recommended hub/drum size for a 13" diameter wheel is one that is for 10" diameter brakes. The wheel will still fit on the hub/drum assuming the bolt pattern matches there is just less surface area on the hub for the wheel. However, you…

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Answer 11

If you have a 2017 Toyota Tacoma with the tow package/factory 7-way yes it is pre-wired for a brake controller. For a brake controller I recommend the Prodigy P3 Brake Controller part #90195. This is our best selling brake controller because of how…

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Answer 12

You said you checked the brake magnets. When inspecting them did you notice if the windings inside the magnets are showing? If so this is most likely the reason that the short is showing up on the controller when the vehicle is moving. This would…

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Testing Electric Trailer Brake Magnets with a Multimeter

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