Ford F series Owner's Manual page 250

To avoid damaging your vehicle or your battery,
and to avoid injury to yourself, follow these
directions for preparing your vehicle to
jump-start and connecting the jumper cables in
the order they are given. If in doubt, call for
road service.
Preparing Your Vehicle
1. Your vehicle has a 12-volt starting system, so
you need to use a 12-volt jumper system.
You will damage your starting motor,
ignition system, and other electrical parts if
you connect them to a 24-volt power supply
(either two 12-volt batteries in series or a
24-volt generator set).
2. Do not disconnect the battery of the disabled
vehicle. You could damage the vehicle's
electrical system.
3. Park the booster vehicle close to the hood of
the disabled vehicle. Make sure the vehicles
do not touch each other. Set the parking
brake on both vehicles and stay clear of the
engine cooling fan and other moving parts.
4. Check all battery terminals and remove any
excessive corrosion before you attach the
jumper cables.
5. Turn on the heater fan in both vehicles.
Turning on the fan helps protect the
electrical system from voltage surges. Turn
off all other switches and lights in both
vehicles to prevent possible damage to either
vehicle's electrical systems.
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