Practice question

On a tractor-trailer with air brakes, what does the red eight-sided trailer air-supply control do?

It controls the tractor parking brakes only
It supplies air to the trailer system when pushed in and exhausts trailer supply air when pulled out
It adjusts the compressor governor
It drains moisture from the trailer reservoir

Answer: B — It supplies air to the trailer system when pushed in and exhausts trailer supply air when pulled out

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