You are coupling a tractor to a semi-trailer. You have backed up but are not yet under it. Before backing under the semi-trailer, you should hook up

A the emergency and service air lines.

Explaination

Before backing under the trailer, you must lock the trailer brakes – which means that you first have to make sure that the trailer brakes are working. Connect the emergency and service air lines and test the trailer brakes.

B the electrical service cable.

C nothing. Back up and lock the fifth wheel.

Select your State

Take more free practice tests for other CDL topics with our cdl prep now!