How to Test Brake Magnet Amperage With Multimeter

Updated 02/21/2012 | Published 02/16/2012

Question:

The article titled Testing Trailer Brake Magnets for Proper Function lists specifications for the DC amp draw for 2, 4, and 6 brakes installed. For example, 4 12 brakes should draw 15 to 16 amps. The article also recommends use of the BTMT15 multimeter, however this multimeter - and most others like it - has a 10A DC range function setting. Does this mean that it allows 0 to 100A in 10A increments, or that it reads 0 to 10A? If it only reads 0 to 10A which is what I thought that setting allows, how does one do the test? Thanks.

asked by: Neal A

Expert Reply:

You are correct, the PT89ZR is only designed to measure up to 10A which will not allow you to measure for 4 or 6 brake magnets on a trailer. In this case I would recommend using a multimeter with a higher amperage rating or testing the magnets separately. At this time we do not carry a multimeter capable of testing more than 10A.

The next section of our brake magnet testing article details how to test each magnet separately to determine if one or more of the brake magnets on your trailer is defective.

To test individual brake magnets for proper function sever the magnet wires and connect 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. Check the amperage, if the amperage is greater than the specified amount then replace the magnet. If the reading is less than the specified amount, the leads are bad and the magnet should be replaced.

expert reply by: John H