Your car will not start, the bonnet is open and you have two jump leads. Which clamp goes on first? The correct jump leads order is more than a colour-matching exercise. It reduces the risk of sparks near the battery and helps protect sensitive electrical equipment. Before touching a terminal, check the vehicle handbook: its designated connection points always take priority.
Jump leads order: the quick answer
For most modern UK cars with compatible 12-volt, negative-earth systems, connect the red lead to the flat battery’s positive (+) terminal first. Connect its other end to the donor battery’s positive (+) terminal. Attach the black lead to the donor battery’s negative (-) terminal. Finally, attach the remaining black clamp to the flat car’s approved earthing point, away from the battery.
Removal is the reverse: black from the flat car’s earth point, black from the donor negative, red from the donor positive, then red from the previously flat battery. This is the usual jump lead connection order, not a substitute for model-specific instructions.
Check these things before connecting
Park the cars close enough for the cables to reach, but never let them touch. Switch off both ignitions and accessories. Apply the handbrakes and select park or neutral. Remove loose metal jewellery, inspect the leads for damage and keep cables away from fans and belts.
Both vehicles must have compatible electrical systems and matching voltage; most ordinary cars use 12 volts. Do not jump-start a battery that is cracked, leaking, swollen, frozen or visibly damaged. If you cannot confidently identify both terminals, stop and call a breakdown professional.
Some vehicles have their batteries in the boot or beneath covers, with dedicated jump-start posts under the bonnet. Use those posts when the handbook specifies them. A battery’s red plastic cover is a clue, but the printed plus and minus markings are the reliable identifiers.
How to connect jump leads in the correct order
1. Red to the flat car’s positive terminal
Find the positive (+) battery terminal or approved positive jump post on the car that will not start. Attach one red clamp firmly, ensuring its metal jaws touch only the intended connection.
2. Red to the donor car’s positive terminal
Connect the other red clamp to the donor battery’s positive (+) terminal or designated post. Keep the loose black clamps away from the red cable, metal bodywork and each other.
3. Black to the donor car’s negative terminal
Connect one black clamp to the working battery’s negative (-) terminal, unless its manufacturer specifies a separate negative point. The final black clamp should still be free.
4. Black to the flat car’s approved earth point
Attach the remaining black clamp to the flat vehicle’s designated earthing point, generally a solid, unpainted metal part of the engine or chassis. Keep it well away from the battery, fuel components and moving parts. Do not guess which bolt is suitable.
Why does the final black clamp go somewhere else?
The last clamp completes the electrical circuit, and a small spark is possible. Lead-acid batteries may release flammable hydrogen gas. Making that final connection away from the flat battery lowers the risk of a spark close to those gases.
Imagine a car with its negative terminal tightly tucked against a plastic casing. Clamping the black lead there may seem easier than finding another point. Instead, look for the marked engine-bay earth post shown in the manual. That small pause is particularly worthwhile when you are rushing to leave a supermarket car park.
Starting the cars after the leads are attached
Once every clamp is secure, follow both vehicles’ instructions. A common method is to start the donor engine and allow it to run for a few minutes before trying the flat car. Keep people and loose cables away from moving engine parts.
Use short starting attempts rather than cranking continuously; the RAC advises no more than about five seconds at a time. If the car fails to start after a few attempts, stop. The fault could involve the battery, charging system or starter rather than insufficient waiting time. Never continue if the leads become hot.
How to remove jump leads safely
After a successful start, follow the manufacturer’s shutdown instructions. The AA recommends switching both engines off before removing the leads. Take off one clamp at a time, keeping it clear of metal and the other clamps.
Remove the black clamp from the flat car’s earth point first. Then remove black from the donor battery’s negative (-) terminal. Next remove red from the donor battery’s positive (+) terminal. Finally remove red from the previously flat battery’s positive (+) terminal.
That is the reverse of the connection sequence. A useful memory aid for the jump cable order UK motorists commonly need is: red goes on first, black goes on last; black comes off first, red comes off last.
Modern cars and situations that need extra care
Cars with start-stop systems may have battery-monitoring sensors and dedicated earth points. Hybrids and electric cars have additional restrictions: never use one as a donor unless its manufacturer expressly allows it. Some hybrids permit jump-starting their 12-volt auxiliary battery, but never interfere with high-voltage equipment.
Do not use this standard sequence for vehicles with different voltages or incompatible earth polarities. Never reverse positive negative jump leads or allow exposed clamps to touch. When instructions are unclear, professional help is safer than experimenting.
What to do once your car starts again
A jump start does not confirm that the battery is healthy. After the leads are off, check that the car restarts as directed by its handbook. A normal drive may put some charge back, but a suitable charger is generally more effective for restoring a deeply discharged battery.
If the battery goes flat again, have the battery and charging system tested. Useful next reads include car battery warning signs, how to charge a car battery and portable jump starter packs. Repeated jump starts are a symptom to investigate, not a lasting fix.
Frequently asked questions
Do you connect positive or negative first?
Connect the positive red cable first on a typical compatible 12-volt car. Attach black to the donor negative next, and make the final black connection at the flat car’s approved earth point.
Can I connect black directly to the flat battery’s negative terminal?
Not as the standard final connection. Use the vehicle’s recommended earth point away from the battery to reduce the chance of sparks near battery gases.
What if I connect the clamps incorrectly?
Wrong connections can cause sparks, short circuits and serious electrical damage. Do not try to start the engines. If you are unsure how to correct the setup safely, call a professional.
Can I take off the cables with both engines running?
Follow the vehicle manuals. The AA advises switching off both engines before disconnecting, then removing the leads in reverse order and checking whether the previously flat car restarts.
The order worth remembering
For a typical compatible car, connect red to the two positive points, black to donor negative and black last to the flat car’s approved earth. Remove everything in reverse. Checking the markings and handbook beforehand matters more than doing the job quickly.