What is the colour coding that is often used for the supply and service lines to the trailer?
- Blue for the supply line and red for the service line
- Red for the supply line and green for the service line
- Red for the supply line and blue for the service line ✓
- Green for the supply line and red for the service line
Answer: C. Red for the supply line and blue for the service line
The supply line is red and the service line is blue.
Why this is the answer
In the coupling section, the handbook lists the industry standard colours for the air lines: blue is for the service line, while red is for the supply or emergency line. That matches the answer that calls the supply line red and the service line blue. When you connect the lines during coupling, use those colours to tell the two lines apart. The handbook does not give any other colour pairing for these lines.
Why the other answers are wrong
- A. Blue for the supply line and red for the service line — This reverses the handbook's colours by making the supply line blue and the service line red.
- B. Red for the supply line and green for the service line — It names green for the service line, but green is not part of the standard colour pairing the handbook gives.
- D. Green for the supply line and red for the service line — It puts green on the supply line and red on the service line; green is not given for either line, and red is the supply colour, not the service colour.
Remember it
Picture red as the emergency air feed and blue as the line that works the brakes.