The correct sequence prevents explosions
The standard jump-start sequence: Red to dead positive, red to good positive, black to good negative, black to unpainted metal on the dead car (not the dead battery's negative terminal).
The final connection is made to engine metal rather than the battery terminal because batteries can vent hydrogen gas. A spark at the battery terminal during connection can ignite the gas. Making the final connection away from the battery eliminates this risk.
Reverse order
Remove cables in reverse order: black from the ground strap first, black from the good battery, red from the good battery, red from the dead battery. Let the jumped vehicle run for at least 20 minutes to recharge.
Beyond a dead battery
If the vehicle cranks but does not start, the problem is not the battery. If the vehicle does not crank at all even with a good jump, the battery may be completely dead or there may be a connection problem (corroded terminals, loose cables). Clean terminals with a wire brush and retry.
- Sequence: red-dead, red-good, black-good, black-ground
- Final black clamp to engine metal, not the dead battery
- Remove in reverse order
- Let the jumped vehicle run 20+ minutes to recharge
- If it cranks but won't start, the problem is not the battery
- Vehicle Safety — NHTSA vehicle maintenance guidance.