If your vehicle has this feature, the control is mounted on the steering column.

This feature lets you apply the trailer brakes without applying the tractor brakes. You can apply the trailer brakes a little or apply them all the way if you have to. Use this control only when you are driving. Do not use it for parking or to hold the rig on a hill.

Caution: Using the trailer brake hand control for parking or for holding the vehicle on a hill may not keep the vehicle from rolling. This can happen if someone hits the valve by accident, or if air pressure bleeds from the system. If the vehicle rolls, you or others could be injured. To park the vehicle or hold it on a hill, use the parking brake properly.