Take a look at
this thread stuck at the top of the page. It will give adjustment procedure complete with pictures. (about 2/3 of the way down the page)
If you are talking about adjusting your electric brake controller in the truck then this is the generally accepted procedure.
1. Drive and apply the brakes several times to get them warmed up.
2. Drive at 25mph and apply the hand controller as hard as it will go.
3. If the brakes lock up, reduce the gain a bit and try again until you get just to the point before lockup.
4. If the brakes will not lock up at maximum gain, do not despair. It is not unusual for electric brake to be unable to lock the wheels on pavement but should do it on sand or gravel. If you get a good strong tug then you should be good to go
5. Keep trying to lock up the brakes with gain adjustments until you get the strongest pull back possible without the wheels locking up. Leave the controller at that point until braking performance diminishes then adjust the brakes and the controller again.
Barney