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Illinois CDL Practice Exam.

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What triggers the visibility of a mechanical arm in the "Wig Wag" device in an air brake system?
Correct Answer:
Air system pressure below 60psi
Explanation:
The visibility of a mechanical arm in the "Wig Wag" device is triggered when the air system pressure drops below a certain threshold, typically around 60 psi. The Wig Wag is designed to alert the driver when the air pressure is insufficient for safe operation. When the pressure falls below 60 psi, the mechanical arm rises, indicating a warning condition. This safety mechanism is crucial as it helps prevent unsafe operation of the brakes due to insufficient air pressure, which could lead to brake failure. Drivers must pay attention to the Wig Wag's warning to ensure they maintain proper air pressure levels in their braking system, which is essential for effective braking performance.

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