Home › CDL Practice Tests › General Knowledge Questions › Question 136
Which glad hand supplies the air that fills the trailer tanks and releases the trailer spring brakes?
- A.The service line with the blue glad hand
- B.The electrical cord
- C.The safety chain hook
- D.The supply (emergency) line, usually fitted with a red glad hand
Correct answer
D. The supply (emergency) line, usually fitted with a red glad hand
Why
The supply line charges the trailer reservoirs and controls the trailer spring brakes through the tractor protection system. The service line carries only the pressure signal created when you press the brake pedal.
Manual topic: Combination Vehicles - Air Lines · From the General Knowledge practice bank (GK-136).