Trailer Brakes Do Not Lock Up and Show Low Voltage, What is the Right Voltage

Updated 02/21/2011 | Published 02/19/2011

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Electric Trailer Brake Assembly - 10" - Right Hand - 3,500 lbs

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Digital Multimeter with 42" Long Test Leads - LED Display

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Question:

Vehicle: 96 Toy 4Runner, can hear brakes hum but wheel will not lock up. Have adjusted trailer brakes, and measured voltage in wire to elect brake: less than one volt, is this correct?

asked by: Ward E

Expert Reply:

I contacted our representative at Redline about the issue you are having with your trailer brakes and your 1996 Toyota 4Runner. He informed me that there should be 12 volts of power at the trailer brakes if the brake controller is putting out 12 volts.

Start with your brake controller. Review the set-up instructions that came with your controller to make sure it adjusted correctly. Then, use a multimeter like part # PT89ZR to check the voltage on the blue output wire of the controller. With the controller turned all the way up, you should get 12 volts on this wire with the manual brake switch activated.

The other thing you will want to check is the connector on the vehicle and the trailer. There could be corrosion in the connector that is preventing sufficient voltage from getting through to the trailer. You can test the voltage at the vehicle side of the connector and at the trailer side connector to see if this is the case. If so, you will need to replace the 7-way connector.

You can also test the brake magnets. I have included a link to an FAQ article that explains how to test trailer brake magnets to see if they are working properly. I will also link you to a video showing how to bench test a brake controller.

expert reply by: Reno H