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Old 09-09-2020, 06:57 AM
  #9  
capt_matt
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Join Date: May 2006
Location: Maryland
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The black box is a resistor that will allow the system to work with brake controllers in older Ford and Chevy trucks. Leave it in place in case the trailer is ever towed by a truck that needs the resistor. Otherwise no brakes!

It sounds to me like your brake controller might be the issue - it is what sends power to the brake pump. If the pump is running it is because the controller is sending power.

Checking the break away switch for a short is a good suggestion. And it is always possible that water or corrosion have caused a short or poor connection.