Ford F series Owner's Manual page 306

Lights and Bulb Replacement
It is a good idea to check the operation of the
following lights frequently:
headlamps
tail lamps
brakelamps
high-mount brakelamp
hazard flasher
turn signals
license plate lamps
The alignment of your headlamps should be
checked if:
oncoming motorists frequently signal you to
turn off your vehicle's high beams when you
do not have the high beams on
the headlamps do not seem to give you
enough light to see clearly at night
the headlamp beams are pointed substantially
away from a position slightly down and to
the right
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