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Question
What is the Johnson bar?
Answers
A.  A hand valve that works the trailer brakes
B.  A valve that indicates the fuel level
C.  A valve that measures the amount of liquid in the air brake system
D.  A valve that allows for the release of excess pressure in the braking system
Explanation
The trailer hand valve, also called the trolley valve or Johnson bar, is used to work the trailer brakes. It should be used only to test the brakes.
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