Never | |
When parked on a grade | |
When parking for less than 10 minutes | |
When unloading |
As soon as you start to jackknife | |
When you start to recover from the jackknife | |
Never | |
In the middle of the jackknife |
Engages the trailer air brakes | |
Prevents trailers from becoming decoupled | |
Supplies air to the cab | |
Supplies air to the trailer |