See Figure 1
It is very important to be careful about running the engine, on vehicles equipped with limited slip differentials, while the vehicle is up on the jack. This is because when the drive train is engaged, power is transmitted to the wheel with the best traction and the vehicle will drive off the jack if one drive wheel is in contact with the floor, resulting in possible damage or injury.
Jack a Ford truck from under the axles, radius arms, or spring hangers and the frame. Be sure and block the diagonally opposite wheel. Place jackstands under the vehicle at the points mentioned or directly under the frame when you are going to work under the vehicle.