2 ptsTOfficial number: 6666
What is the colour of the control cable in trailers with a two-circuit pneumatic braking system?

Explanation
Correct answer: Yellow.
Dual-circuit pneumatic braking systems in trailers use standard colour coding to prevent incorrect connection. The supply line (which delivers compressed air to the trailer's system) is red, whereas the control line (which transmits the braking signal from the towing vehicle) is yellow.