Ford Mustang Owner's Manual page 209

Do not work on a vehicle in an enclosed
space with the engine running, unless you are
sure you have enough ventilation.
Never get under a vehicle while it is
supported only by a jack. If you must work
under a vehicle, use safety stands.
Keep all lit cigarettes and other smoking
materials away from the battery and all
fuel-related parts.
If you disconnect the battery, the engine must
"relearn" its idle conditions before your vehicle
will drive properly. To find out how the engine
does this, see Battery in this chapter.
Working with the engine off:
1. Set the parking brake fully, block the wheels,
and make sure that the gearshift is securely
latched in P (Park) (automatic transmission)
or 1 (First) (manual transmission).
2. Remove the key from the ignition after you
turn the engine off.
3. Block the wheels. This will prevent your
vehicle from moving unexpectedly.
Working with the engine on:
1. Set the parking brake fully, and make sure
that the gearshift is securely latched in P
(Park) (automatic transmission) or Neutral
(manual transmission).
2. Block the wheels. This will prevent your
vehicle from moving unexpectedly.
Do not start your engine with the air
cleaner removed and do not remove it
while the engine is running.
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