Troubleshooting Large Voltage Drop On Trailer Brake Wiring When Bypassing With Battery Power
Updated 05/05/2023 | Published 05/04/2023
Question:
I have a 20t trailer with e-brakes on both axels. I have replaced three of the four brakes due to seals going out or magnet failure. I am trying to get the tires to lock up but even with max gain they keep rolling. I have not seated them in ,but I have never had to do this to any other brakes either on trailers or trucks. I am also loosing voltage, I am going from 13.2 volts to about 9 volts at any brake when they are applied. I am using a separate battery and have the same result as when using the trucks brake controller. The truck is a 2020 Ford F550. Please let me know what your suggestions or ideas are to fix this problem. We do have a twin to this unit and it is not having any problems, we have not had to do the brakes yet on this trailer. Thanks
asked by: Paul T
Expert Reply:
It sounds like you likely have a damaged wire on your trailer for the brakes. Since you are seeing large voltage drop at the brakes even when connecting to a battery this is the only explanation. I recommend doing a similar test of connecting 13.2 volts power to the trailer brakes and checking along the brake wire to see if you can determine exactly where you see a large drop. Typically a 10% drop is okay but larger is sign of damaged parts. A test light like the # PTW2992 is great as it allows you to see voltage and has a small tip to pierce into wiring.
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