Unfortunately since the internet has so much damned censorship and people charge for a simple question, my best answer for you is to try and purchase a book for your vehicle.
Do you mean a SCHEMATIC diagram?
You can find a 1981 Ford F150 manual transmission diagram inside the vehicle's owner's manual. Some auto stores also have the diagram available.
Where can you find a audio wiring diagram for a 1994 Ford F150?
Autozone
In your car manual
When making changes to any part of a car, a diagram will help the person know what to do. A diagram for a 1995 Ford F150 front suspension can be found in the maintenance manual of the car.
You can find a full illustration diagram for a 93 Ford F150 automatic locking hub in the truck's owner's manual. You can also find it at various auto stores.
You can find a vacuum diagram, for your 1992 Ford F1 50 pickup truck, at most Ford dealerships. You can also find the diagram at most auto-parts stores.
When working on an engine it is important to have a diagram to help a person recognize the parts. A diagram for a Ford Tempo Engine is found in its manual.
You can find a fuel tank assembly diagram for your Ford F1 50 pickup truck at most Ford dealerships. Ford service manuals will have the fuel tank assembly diagram and can be found at your local library.
You can find an engine diagram for a 2003 Ford Expedition in the vehicle's owner's manual. You can also find it at certain auto stores.
When working on a car, it is important to have a diagram on hand. A diagram for a 1997 Ford Explorer Engine can be found in the maintenance manual.