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Diagnosing Trailer Brake Problem on 16 Foot Dual Axle Trailer Pulled by 1979 Jamboree Motor Home


I have a 79 Jamberee w/ a 16 dual axial trailer. I can hear the soleniods humming when the brakes are applied, but the trailer brakes arent working. Even when appling the manual override. Ive made sure the 90 degree taggle is 90 to the road. and rotated the max/min dial back and forth w/no luck.


Expert Reply:

Are you hearing the brake controller humming, or the brake magnets on the trailer?

Use a multimeter like part # PT89ZR to test the voltage on the blue wire exiting the rear of the controller while the override switch is activated. If the controller is set for maximum power, you should see close to 12-volts.

Then test the brake output pin at the trailer connector. For a 6-way, it will be the pin in the 10:00 position. For a 7-way, it will be the pin in the 5:00 position. Once again, with the override activated and the controller turned all the way up, you should be seeing around 12-volts. Then check the voltage on the brake wire feeding the brake magnets. You should get as close to the brake assembly as possible. Check the electrical connections at the brake magnets. Once lead from each magnet should be grounded to clean metal on the trailer frame, the other should be attached to the brake wire.

If all this checks out, make sure your trailer brakes are correctly adjusted. I will link you to a video showing how this is done. Fast forward to the 4:48 mark.

Finally, check to make sure the brake magnets are not excessively worn. Pull the drums off, and examine the face of the magnet that rides along the inside of the brake drum. If you can see the copper windings in the face of the magnet, it will need to be replaced.

I have linked you to our Wiring FAQ page, as well as some videos that will help diagnose your problem.

expert reply by:
Mike L

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