Mercury Mountaineer 2009 Owner's Manual page 745

Roadside Emergencies
3. Connect the negative (-) cable to the negative (-) terminal of the
assisting battery.
4. Make the final connection of the negative (-) cable to the ground stud
located toward the front of the vehicle (forward of the battery) on the
radiator support. Keep the negative (-) cable away from the battery and
the carburetor/fuel injection system. Do not use fuel lines, engine rocker
covers or the intake manifold as grounding points.
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2009 Mountaineer (mnt)
Owners Guide, 1st Printing
USA (fus)