To jump start a car, connect the red clamp to the dead battery’s positive terminal, the other red clamp to the good battery’s positive terminal, the black clamp to the good battery’s negative terminal, and the last black clamp to bare metal on the dead car’s engine, away from the battery. Run the good car for a few minutes, then start the dead one. That is how to jump start a car in one paragraph; the rest of this guide covers why the order matters, how jump packs differ, the cars that need special care, and when not to try at all.
Before You Start: Check the Battery and the Cars
Look at the dead battery first. If the case is cracked, swollen, or leaking, or you smell rotten eggs, do not jump it; a damaged battery can vent gas that ignites from a spark. Replace it or have the car towed instead. Also check that the problem is likely the battery: a slow crank, a rapid clicking, or no dash lights at all usually means yes.
Park the good car close enough for the cables to reach without the cars touching. Turn both cars off, set both parking brakes, and put both in park or neutral. Turn off headlights, the radio, and the climate fan on both cars, and unplug anything from the power outlets.
Step by Step With Jumper Cables
Clamp one red (positive) end to the positive terminal on the dead battery, marked with a plus sign or a red cover. Clamp the other red end to the positive terminal on the good battery. Clamp one black (negative) end to the negative terminal on the good battery. Clamp the last black end to a bare, unpainted metal bolt or bracket on the dead car’s engine block, a foot or more away from the battery.
That last connection is the one most people get wrong. Clamping it straight to the dead battery’s negative terminal works electrically, but it puts the final spark right next to the battery, where hydrogen gas can collect. A ground point away from the battery keeps the spark away from the gas.
Starting the Car and Removing the Cables
Start the good car and let it run for three to five minutes so it puts some charge into the dead battery. Then try the dead car. If it starts, leave both running for a minute, then remove the cables in the exact reverse order: black from the engine ground, black from the good battery, red from the good battery, red from the formerly dead battery. Do not let the clamps touch each other or any metal while either is still connected.
Drive the jumped car for at least twenty to thirty minutes, ideally on the highway rather than in stop-and-go traffic, so the alternator can recharge the battery. If it dies again the next morning, the battery needs replacing.
Using a Portable Jump Pack
A charged jump pack replaces the second car. Connect the red clamp to the dead battery’s positive terminal and the black clamp to a ground point on the engine, then turn the pack on and start the car. Most packs have reverse-polarity protection that refuses to power up if the clamps are on the wrong terminals, which makes them safer than cables for most drivers.
Keep the pack charged; one that has sat in the trunk for a year is often as dead as the battery. Commercial packs carried on tow trucks are larger and regulated for modern electronics, which is why our jump start service in Santa Cruz uses packs rather than cables between two cars.
Hybrids, EVs, and Start-Stop Cars
Hybrids and electric cars have a small 12-volt battery that powers the computers and lets the car wake up. When it dies, the car will not turn on, even with a full high-voltage battery. Many of these cars have dedicated jump terminals under the hood or in a fuse box, rather than at the 12-volt battery itself, which may be in the trunk or under a seat. The owner’s manual shows where.
Never connect anything to the orange high-voltage cables or components. Many hybrids and EVs are also not designed to jump another car, so check the manual before using one as the donor. Cars with start-stop systems often use AGM batteries that prefer a regulated pack over a jump from another running car.
When Not to Jump Start a Car
Do not jump a battery that is cracked, leaking, swollen, or frozen. Do not jump a car where the cables would have to cross moving parts like fans or belts. Do not keep trying if the car clicks once and goes silent, cranks but never fires, or starts and dies as soon as the cables come off; each of those points to something other than a flat battery, such as a starter, a fuel problem, or an alternator.
If you are not sure what the symptoms mean, our guide to what to check when your car won’t start explains what each sound tells you. Jumping a car that has a different problem only drains the donor battery too.
If the Jump Does Not Work
Check the clamps first. Corroded terminals, a clamp on painted metal, or thin cheap cables can all stop current from reaching the starter. Clean the terminals with a wire brush if you have one, reseat the clamps, and let the good car run a few more minutes before the next attempt. Two or three tries is enough; more than that and the problem is elsewhere.
When the battery will not take a charge or the car still will not start, roadside assistance with a commercial jump pack and a battery tester can tell in a minute whether it is the battery, the alternator, or the starter, and a flatbed can take the car to a shop if the jump is not the answer.
Jump Start Questions Santa Cruz Drivers Ask
What order do you connect jumper cables?
Red to the dead battery’s positive, red to the good battery’s positive, black to the good battery’s negative, and black to bare metal on the dead car’s engine. Remove them in the reverse order.
How long should I let the car run after a jump start?
At least twenty to thirty minutes of driving, preferably at steady speed, so the alternator can recharge the battery.
Can a jump start damage my car?
It can if the cables are reversed or a clamp sparks near the battery. Following the correct order and using a pack with reverse-polarity protection avoids most problems.
Can you jump start a hybrid or electric car?
Yes, through the 12-volt system and usually at dedicated jump terminals shown in the owner’s manual. Never connect to high-voltage components.
Why won’t my car start even after a jump?
The battery may have a dead cell, or the problem may be the starter, the alternator, or fuel. A battery and charging test will tell which.
If you would rather not handle cables yourself, or the jump did not work, call (831) 464-1155. A truck with a regulated jump pack and a battery tester can reach you anywhere in Santa Cruz County, 24 hours a day.
