Ford Mercury Villager 1997 Owner's Manual page 274

Connecting the jumper cables
1. Connect one end of the first jumper cable to the positive (+)
terminal of the discharged battery. (You can connect either
jumper cable to the positive (+) terminal, as long as you use the
same cable for both positive terminals.) Most jumper cables
have a red cable and a black cable. The red cable is generally
used for the positive terminals and the black for the
negative cable of the booster battery and ground on the engine
of the disabled vehicle.
2. Connect the other end of the first cable to the positive (+)
terminal of the booster battery.
3. Connect one end of the second cable to the negative (–)
terminal of the booster battery — NOT to the discharged battery.
4. Connect the other end of the second cable to a good metallic
surface on the engine or frame of the disabled vehicle.
Do not connect the end of the second cable to the negative
(–) terminal of the battery to be jumped. A spark may
cause an explosion of the gases that surround the battery.
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WARNING