Home › CDL Practice Tests › General Knowledge Questions › Question 109
How can you tell the trailer air supply control apart from the parking brake control in most cabs?
- A.The trailer supply knob is red and eight-sided, while the parking brake knob is yellow and diamond-shaped
- B.The trailer supply is a foot pedal on the floor
- C.The parking brake knob is blue and round
- D.Both knobs are identical and unlabeled
Correct answer
A. The trailer supply knob is red and eight-sided, while the parking brake knob is yellow and diamond-shaped
Why
Control knobs are shaped and colored by standard so you can identify them by touch. Pulling the red trailer supply knob cuts air to the trailer and applies its spring brakes, while the yellow knob controls the tractor parking brakes.
Manual topic: Air Brakes - Brake Controls · From the General Knowledge practice bank (GK-109).