Troubleshooting Trailer Brake Magnets on 12 Inch Brake Assemblies

Updated 09/14/2012 | Published 09/12/2012

Question:

I am getting a ohms reading of 3.7 on my 12x2 inch dexter breaks do I need to replace the magnets

asked by: Herman L

Expert Reply:

Brake magnets for 12 inch brake assemblies should have an ohms reading that falls within the range of 3.0 to 3.8. The 3.7 ohms reading on your brake magnets does not indicate that the brake magnets need to be replaced.

If you are experiencing problems with your trailer brakes, then there are a few other tests that you can run to try and find the problem. First, with the tow vehicle connected to the trailer, connect a multimeter inline with the brake wire somewhere between the trailer connector and the trailer brakes. If your trailer only has 2 brakes, then the amps should read 7.5 to 8.2 at 12 volts. For 4 brakes, 15 to 16.3 amps and for 6 brakes, 22.6 to 24.5 amps. If your amperage reading is greater or less than the specified range for your brakes, then the magnets may need to be replaced.

The next test is to test the brake magnet individually. Testing individual brake magnets for proper function can be accomplished by severing the magnet wires and connecting the ammeter between the positive terminal of a 12 volt battery and one of the magnet wires, it does not matter which one, then connect the other magnet wire to the negative battery terminal. Each brake magnet should read 3.2 to 4.0 amps at 12 volts.

To test the magnet for a short, touch the base of the brake magnet to the negative post of a 12 volt battery. Then, connect one of the brake magnet wires to the negative lead of a multimeter, and the positive lead of the multimeter to the positive post of the battery. If any amperage is detected the magnet is shorted and will need to be replaced.

I have attached an article on testing brake magnets for you to check out.

expert reply by: John H