Checking Air Lines and Electrical Cords
Checking Air Lines and Electrical Cords
This domain tests color coding, connection quality, routing, and the operational checks that prove the rear trailer is receiving air and electricity.
Core rules
- Use the standard color code: blue is the service line for the rear trailer, red is the emergency line for the rear trailer, and green is the electrical cord.
- Match color to color. Crossed lines can release trailer brakes when you apply the foot brake, or cause the brakes to drag.
- Inspect glad hands for missing seals, cracked rubber, and bent locking tabs. Connect firmly and check for leaks by listening or with soap solution.
- Route lines with enough slack for turns but not so much that they drag or chafe. Keep them off the dolly frame, landing gear, and exhaust.
- Check the green cord for cracked insulation, corroded pins, and a loose plug. Confirm tail, brake, turn, and marker lamps on the rear trailer.
- Test the emergency line: disconnect it and confirm the rear trailer’s spring brakes apply. Reconnect and build air pressure before moving.
Worked example
You connect the dolly’s blue line to the front trailer’s red glad hand. When you press the brake pedal, the rear trailer brakes release instead of apply, and the combination rolls. The color code is not cosmetic; it tells you which line carries service air and which carries emergency air. Reconnect blue to blue and red to red, then recheck brake operation.
Traps
- Treating the color code as optional.
- Connecting lines before checking seals.
- Leaving a glad hand seal out or doubled.
- Routing lines tight enough to pull apart in a turn.
- Checking only the front trailer’s lights.
- Not testing the breakaway or emergency function.