How to Test Trailer Brake Magnets on a 2005 Aliner Sport Trailer

Question:

I installed new brake magnets last year Trailer Brake Magnet Kit for 7 Hub/Drums Dexter Accessories and Parts Code: BP01-068 I was checking them recently because it didnt seem like there was much braking going on even with the Prodigy set as high as it would go. I realize that there is not much braking to expect on a 7-in hub but... Anyway, when I jacked up the left side and spun the wheel and activated the brake controller, the wheel stopped spinning abruptly. When I tried the same thing on the right side, the wheel continued to spin. I checked the wiring for continuity and it appears that I have good continuity right up to the magnet. Could I have a bad magnet? Can you recommend another test? Thanks. Love your expert advice and video instruction! 2005 Aliner Sport

asked by: George S

Expert Reply:

Since the brake magnet is new on the side that is not working, there are some other tests that you can do to determine if the magnet is bad. I refer you to an FAQ article I have linked on testing brake magnets.

First, you will need a multimeter, like # PT89ZR if needed, and a separate battery (for some of the tests). The trailer should NOT be connected to the tow vehicle when performing the tests that require a separate battery, unless the magnet has been completely removed from the trailer.

Start by testing for the correct amperage. For a single axle with 7 inch brakes at 12 to 13 volts, you should get a reading of 6.3 to 6.8 volts if testing with trailer connected and using the multimeter on the blue wire as described in the FAQ. To test a single magnet, remove the magnet and use the separate battery and follow the Testing Individual Brake Magnets section. If the readings are too high or too low, the magnet(s) will need to be replaced.

To test for a short, disconnect the battery negative wire from the brake magnet wire and connect the base of the brake magnet to the battery negative post. If there is any amperage the magnet is shorted and will need to be replaced.

To check the resistance, switch to the ohmmeter setting of the multimeter. For a 7 inch brake magnet, the resistance should read 3.8 to 4.0 Ohms. If the resistance is not within the specified range the magnet will need to be replaced.

expert reply by: Michael H