Ford F series Owner's Manual page 20

NOTE: If your light truck is equipped with
dual fuel tanks, the "CHECK ENGINE"
light may come on if fuel is restricted
to the engine or if the fuel flow is
momentarily disrupted because of an
empty fuel tank before you switched to
the auxiliary fuel tank. This condition
is normal and the light should go off
after full fuel flow is restored.
Charging System Light
This light indicates that your battery is not being
charged and that you need to have the electrical
system checked.
Charging system light
This light illuminates every time you turn the
ignition to the ON or START position (engine
off). The light should go off when the engine
starts and the alternator begins to charge.
If the light stays on or illuminates when the
engine is running, have the electrical system
checked as soon as possible.
Battery Voltage Gauge (Voltmeter)
This gauge shows you the battery voltage when
the ignition key is in the ON position.
If you are running electrical accessories (when
the engine is off, or idling at a low speed), the
pointer may move toward the lower end of the
normal band. If it stays outside the normal band
area, have your vehicle's electrical system
checked as soon as it is safely possible.
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