Connecting jumper leads is a straightforward process: attach the red clamp to the positive terminal of the dead battery, the red clamp to the positive terminal of the working battery, the black clamp to the negative terminal of the working battery, and finally the black clamp to an unpainted metal surface on the dead car's engine. Start the working car, wait a few minutes, then start the dead car. Remove the clamps in reverse order once both engines are running.
Key Takeaways
- Red clamps connect to positive terminals (marked + or red), and black clamps connect to negative terminals (marked − or black), with the final black clamp going to bare metal on the engine block rather than the battery itself.
- The order of connection matters: dead battery positive first, working battery positive second, working battery negative third, and engine ground last prevents sparks near the battery.
- You need a working vehicle parked close enough that the leads reach both batteries, jumper leads in good condition with no cracks or exposed wire, and both cars turned off before you begin.
- Removal order is the reverse of connection order, starting with the black clamp on the dead car's engine, then the black clamp on the working car, then both red clamps.
- If the dead car does not start after five minutes of the working engine running, stop and wait longer or seek roadside information rather than repeatedly attempting to start.
What you need before you start
Gather a set of jumper leads (also called jump leads or jumper cables), a working vehicle with a charged battery, and a second person if possible. The leads should be at least 4 metres long so they reach between two cars parked front-to-front or side-by-side. Check that the insulation on the leads is not cracked, split, or peeling, and that the metal clamps close firmly without wobbling.
Both vehicles must be turned off before you connect anything. Open the bonnet of both cars and locate the battery terminals. The positive terminal is marked with a + symbol or a red plastic cover; the negative terminal is marked with a − symbol or a black plastic cover. On the dead car, you may need to remove a plastic cover by hand or with a flat screwdriver to expose the terminal underneath.
The correct order of connection
Start with the dead battery. Attach the red clamp firmly to the positive terminal — you should hear or feel a click as it grips. Do not skip this step or attach it to the negative terminal by mistake.
Move to the working car. Attach the second red clamp to its positive terminal with the same firm grip. Then attach the black clamp to the negative terminal of the working battery.
Finally, attach the remaining black clamp to a bare metal surface on the engine block of the dead car — not to the negative terminal of the dead battery itself. Look for an unpainted bolt, bracket, or flat metal area on the engine. This final connection to ground rather than to the battery terminal reduces the risk of a spark igniting battery gases.
Starting the cars and waiting
Once all four clamps are attached, start the working car and let it run for two to three minutes. This allows charge to flow into the dead battery. Do not rev the engine; normal idle speed is sufficient.
After waiting, attempt to start the dead car. If it starts, leave both engines running for another minute or two before you disconnect anything. If it does not start, wait another two to three minutes with the working car still running and try again. Do not attempt to start the dead car more than three or four times in succession, as this drains the working battery and can damage the starter motor on the dead car.
If the car still will not start after five minutes of the working engine running, stop and wait longer or contact roadside information. Continuing to attempt starting may indicate a problem beyond a flat battery.
Removing the leads in the correct order
Removal order is critical and is the reverse of connection order. Start by removing the black clamp from the engine block of the dead car. Then remove the black clamp from the negative terminal of the working car. Next, remove the red clamp from the positive terminal of the working car. Finally, remove the red clamp from the positive terminal of the dead car.
This reverse sequence prevents a spark from occurring near either battery. Once all clamps are off, close the bonnets of both cars and allow the previously dead car to run for at least twenty minutes so its alternator can recharge the battery.
Common mistakes to avoid
Connecting the black clamp to the negative terminal of the dead battery instead of to engine ground is the most frequent error. This creates a spark risk and can damage the battery. Reversing the red and black clamps — attaching red to negative or black to positive — will not start the car and may damage the electrical system of one or both vehicles.
Removing the clamps in the wrong order can cause a spark. Pulling the leads off too quickly or yanking them rather than unclipping them can bend the clamp terminals and damage the battery posts. If a clamp feels stuck, wiggle it gently side to side rather than pulling straight up.
Attempting to jump-start a battery that is visibly cracked, leaking, or swollen is unsafe. If the dead battery shows any of these signs, do not connect leads to it; contact roadside information or a mechanic instead.
When jump-starting will not work
Jump-starting works only if the battery is flat but not damaged. If the car has not been driven in months, the battery may be too deeply discharged to accept a charge. If the battery is old (more than five years), it may have failed internally and cannot hold charge even after jump-starting.
If the car makes no sound when you turn the key — no clicking, no cranking, no dashboard lights — the problem may be a loose battery cable rather than a flat battery. Check that both battery cable connections are tight before attempting to jump-start. If the car cranks but will not turn over, the problem is likely the engine or fuel system, not the battery, and jump-starting will not help.
Frequently Asked Questions
Can I jump-start a car with the engine running?
No. Both cars must be off when you connect the leads. Connecting leads to a running car can damage its electrical system and the alternator. Turn off the working car before you attach the first clamp.
What if I connect the red and black clamps backwards?
Stop when ready and remove all clamps. Reversed polarity can damage the alternator, starter, or battery of either vehicle. Check the terminal colours and the clamp colours before reconnecting. If you are unsure, wait for roadside information.
How long should I wait before trying to start the dead car?
Wait at least two to three minutes with the working car running at idle. This gives the dead battery time to accept charge. If the car does not start after the first attempt, wait another two to three minutes before trying again.
Do I need to remove the battery from the car to jump-start it?
No. Jump-starting works with the battery in place. Removing the battery is unnecessary and creates more work. straightforward open the bonnet and connect the leads to the terminals as they sit.
Is it safe to jump-start a battery in the rain?
Yes, as long as water is not pooling directly on the battery terminals or clamps. Wipe the terminals dry with a cloth before connecting the leads. Avoid touching the metal clamps together or letting them touch the car body while they are connected to the batteries.