1996 Ford F150 Owner's Manual - Page 264

If you have a four-wheel drive vehicles with manual locking hubs, put transfer case lever in 2H, 4H, or 4L. When one of the back wheels is off the ground, the transmission alone will not prevent the vehicle from moving or slipping off the jack, even if the vehicle is in P (Park) or 1 (First). To prevent the vehicle from moving when you change a tire, be sure the parking brake is set, then block the wheel (both directions) that is diagonally opposite (other side and end of the vehicle) to the tire that is being changed. RWARNING If the vehicle slips off the jack, you or someone else could be seriously injured. When the transfer case is in the N (Neutral) position, the engine and transmission are disconnected from the rest of the driveline. Therefore, the vehicle is free to roll even if the automatic transmission is in P (Park) or the manual transmission is in gear. RWARNING Do not leave the vehicle unattended with the transfer case in the N (Neutral) position. Always set the parking brake fully and turn off the ignition when leaving the vehicle. 263