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Testing for Proper Voltage on the Brake Output Circuit

Question:

What should voltage output from plug on vehicle be going to trailer brakes. Mine is .2 V.

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Expert Reply:

There are many things that can affect the voltage on the brake output wire from your brake controller to your trailer brakes such as the power setting on your brake controller, how you are testing the wire and if you are testing it with the brakes or manual override activated.

Using a multimeter to test the voltage on the brake output wire at your trailer connector will not always give the proper reading because it does not provide a load on the circuit like brake magnets from a trailer would. Instead of using a multimeter, I recommend using a circuit tester like part # PTW2979. This circuit tester has an incandescent bulb that will apply a load to the circuit that will allow full power to be applied on the wiring.

To test for proper voltage on the brake output wire, set the power gain on your brake controller to the maximum. Have someone apply the manual override on the brake controller while you use a circuit tester to test the pin on the trailer connector for the trailer brakes. If the light is bright, then you know you are getting full voltage.

If you are experiencing poor braking with full voltage, then the issue is likely on the trailer. Make sure your trailer brakes are adjusted properly and you could also check your brake magnets. I have attached an FAQ article on testing your brake magnets for you to check out if you feel that this is a possible issue.

If the 0.2 volts that you are getting is when the brakes are not being applied then that is the signal that the brake controller sends back to the brake magnets to detect if a trailer is connected or not.

If the light is dim when the manual override is applied, then we will need to do further troubleshooting. I would first check that all of the wires from the brake controller (ground, 12 volt power, stop light switch) are properly connected. If all of the connections look secure, then you can cut the blue wire about 6 inches back from the brake controller to test for voltage there. If you have full voltage at that point, we know there is an issue on the brake output circuit somewhere between that point and the trailer connector. Check the vehicle side trailer connector for corrosion or a poor ground connection and you should also check the brake output wire for any damaged sections that could cause a drop in voltage.

If you do not have the proper voltage at that point, the brake controller is likely bad and will need to be replaced. If you determine that a replacement is necessary, I would recommend the Tekonsha Prodigy P2, # 90885. This is a proportional brake controller that will provide a smooth ride by applying the trailer brakes with the same intensity as the tow vehicle.

If you are unable to find the problem or a solution after following these steps, let me know what you come up with and we can do further troubleshooting.

expert reply by:
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John H

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