Ford F series Owner's Manual page 74

Variable Interval Wipers
In addition to two speed wipers, your vehicle is
equipped with wipers that you can set to
operate at varying intervals. For example, you
can set the interval so they wipe less often when
it drizzles or more often in heavier rain.
Interval wiper on turn signal lever
To set the interval wipers, rotate the knob at the
end of the turn signal lever toward or away
from the instrument panel to the interval
operation you desire.
Windshield Washer
To clean the windshield, push in the end of the
wiper knob. For a constant spray, keep the knob
pushed in. After you release the knob, the
wipers operate for two to three cycles before
turning off (if wipers were off) or returning to
the selected setting.
Do not try to clean the windshield when the
washer fluid container is empty or activate the
washers at any time for more than 15 seconds
continuously. This could damage the washer
pump system.
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