Mercury 2000 Grand Marquis Owner's Manual page 146

Roadside emergencies
2. Connect the other end of the positive (+) cable to the positive (+)
terminal of the assisting battery.
3. Connect the negative (-) cable to the negative (-) terminal of the
assisting battery.
4. Make the final connection of the negative (-) cable to an exposed
metal part of the stalled vehicle's engine, 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.
146