What is the colour coding that is often used for the supply and service lines to the trailer?
- Red for the supply line and green for the service line
- Red for the supply line and blue for the service line ✓
- Blue for the supply line and red for the service line
- Green for the supply line and red for the service line
Answer: B. Red for the supply line and blue for the service line
The supply line is red, and the service line, also called the control line, is blue.
Why this is the answer
The handbook says glad hands are often colour-coded. It states that blue colouring indicates the control line, which is also commonly called the service line. It also states that red is used to indicate the supply line. Putting those two colour codes together gives red for the supply line and blue for the service line, which matches the bank answer.
Why the other answers are wrong
- A. Red for the supply line and green for the service line — Green is not the colour the handbook gives for the service line; the service line is shown in blue.
- C. Blue for the supply line and red for the service line — This reverses the handbook's coding, because blue marks the service or control line, not the supply line.
- D. Green for the supply line and red for the service line — This also reverses the coding and adds green; the handbook gives red for the supply line and blue for the service line.
Remember it
Remember red for the air supply and blue for the control signal to the trailer brakes.