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Troubleshooting Weak Trailer Brakes and Breakaway Switch that Doesnt Work at All


My trailer brakes only partially come on when brakes applied and they wont come on at all when break away pin is pulled.


Expert Reply:

It sounds like you need to check the trailer braking system out. I would start by making sure that the connectors on the vehicle and trailer are connected properly, and that there is no corrosion in either of the connectors. Corrosion can rob power from the trailer brakes especially because the trailer brake circuit is in the lower position in the connector and next to the ground wire. Using some dielectric grease, item # 11755, in the connection can often help a great deal.

Make sure that the ground wires to the trailer brake magnets are properly grounded too.

There are several checks that can be performed if the issue is not solved. First, make sure that the brakes are adjusted properly. We have a video detailing how to adjust the trailer brakes for you to review.

Next, if the brakes are adjusted properly you can check the brake magnets, this will require that you sever the wires near the backing plate of the brake assembly. Using an ohmmeter, item # PT89ZR, check the resistance between the brake magnet wires, 10 and 12 inch brake magnet resistance should be 3.2-3.5 Ohms, and 7 inch brake magnet resistance should be 3.8-4.0 Ohms. If the resistance is too low or too high the magnets will need to be replaced, see link. Another method of testing the brake magnet is detailed in our Diagnosing a Trailer Magnet Problem video, see link.

Finally, the brakes themselves may be worn or the hub may need to be resurfaced or replaced. If there are grooves in the hub where the brakes ride on the hub or where the magnets connect to the hub repair or replacement will be needed. You will need to remove the hubs to check these areas.

If you determine that the hubs need to be replaced, let me know the inner and outer bearing numbers, the seal number and the wheel bolt pattern. I will be glad to help find the correct parts for your trailer.

Is your breakaway battery charged? If so, you should check out the picture I attached that shows how it should wire up and make sure yours is wired the same.

click to enlarge
expert reply by:
Jameson C

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