Practice question

In a tractor-semitrailer pneumatic coupling, what are the functions of the two standard glad-hand air lines connecting the tractor to the trailer?

  1. One line carries diesel fuel and the other carries coolant
  2. The RED line is the Emergency / Supply line (charges trailer tanks and releases spring brakes), and the BLUE/YELLOW line is the Service line (transmits pedal braking signals)
  3. Both lines are identical electrical grounding wires
  4. One line operates the windshield wipers and the other operates horn horns

Answer: B — The RED line is the Emergency / Supply line (charges trailer tanks and releases spring brakes), and the BLUE/YELLOW line is the Service line (transmits pedal braking signals)

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