Ford F-150 Owner's Manual page 277

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.
2007 F-150 (f12)
Owners Guide (post-2002-fmt)
USA (fus)
Roadside Emergencies
277