Flashcard 11 - Combination Vehicles Flashcard Set for the CDL

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The correct answer is:

The service line (blue) is used to signal the relays in the trailer brakes. The relays supply air from the air tanks to the brake cylinders, which apply the brakes. The service line is controlled by the foot brake or the trailer hand brake.


Explanation:

The emergency line (red) charges the air tanks and is part of the emergency braking system.

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