Ford 2008 F-150 Owner's Manual page 301

To reinstall the fuse box cover, place the top part of the cover on the
fuse panel, then push the bottom part of the cover until you hear it click
shut. Gently pull on the cover to make sure it is seated properly.
Always disconnect the battery before servicing high current
fuses.
To reduce risk of electrical shock, always replace the cover to
the Power Distribution Box and Auxiliary Relay Box before
reconnecting the battery or refilling fluid reservoirs.
If the battery has been disconnected and reconnected, refer to the
Battery section of the Maintenance and Specifications chapter.
The fuses are coded as follows.
2008 F-150
Owners Guide (post-2002-fmt)
USA
Roadside Emergencies
301