Which colour is the trailer supply line?
- White
- Yellow
- Blue
- Red ✓
Answer: D. Red
The trailer supply line is red.
Why this is the answer
The coupling section of the truck handbook lists the industry standard air-line colours: blue for the service line and red for the supply or emergency line. Since the question asks for the trailer supply line, the colour that matches the handbook is red. The other listed colours either belong to a different air line or are not given as air-line colours in the passages.
Why the other answers are wrong
- A. White — The passages do not list white as the trailer supply line colour; the handbook gives red for supply or emergency and blue for service.
- B. Yellow — The passages do not list yellow as the trailer supply line colour; the handbook gives red for supply or emergency and blue for service.
- C. Blue — Blue is the service line colour in the handbook, not the supply or emergency line.
Remember it
Remember the pair from the handbook: red handles supply or emergency, blue handles service.