SGI Class 1 Practice Questions - Saskatchewan Class 1 Commercial Driver Licence Written Exam

What is the purpose of the 'johnny light' or hand valve in a tractor-trailer?

To turn on the trailer's interior lights To apply the trailer service brakes independently of the tractor brakes To drain condensation from the primary air tank To lock the sliding fifth wheel into position

Correct Answer:

To apply the trailer service brakes independently of the tractor brakes

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