Using jump leads

How to use jump leads without hurting yourself or damaging either car

Check the vehicle handbook before using jump leads

Unless you know what you're doing, delving under the bonnet to check for or correct faults can be dangerous. We generally recommend that you seek professional assistance.

Check the vehicle handbook before using jump leads. All include general advice on jump-starting but some include model specific procedures. If this is the case you must follow the manufacturer's procedure rather than the steps described below.

Jump starting a vehicle can be a safe procedure however and damage can be avoided if a few simple rules are followed:

Safety rules

Keep metal objects out of the way – rings, watch straps, hand tools, clips or stray wires just brushing a battery post can cause a spark, possibly exploding the battery and releasing the acid.

Don't attempt to jump-start a battery that is leaking or looks damaged – it could explode.

Avoid smoking or naked flames – batteries give off flammable gases so an explosion could result.

Keep hands well away and avoid loose fitting clothing, particularly scarves or neckties – with the engine running it's easy to get caught-up and seriously injured on moving parts like pulleys or belts.

Don't use jump leads if they're damaged – broken conductors or damaged clamps can overheat and may catch fire.

Step by step

Before connecting any leads make sure the vehicles are the same voltage and that they're parked with their handbrakes on and ignition off. The vehicles must not touch as this can cause sparks or an explosion.

Use the red jump lead to connect the positive terminal of the donor vehicle's good battery to the positive terminal of the flat battery.
Then use the black lead to connect the negative terminal of the good battery to a suitable earthing point on the engine or chassis of the other vehicle. This earthing point must be away from the battery and fuel system.
With both leads connected wait three minutes for the voltages to equalise before starting either engine.
Start the engine of the donor car and allow it to run for a minute.
With the donor car engine still running, start the engine of the other car and leave both running at a fast idle for ten minutes.
Don't remove the jump leads while the engines are running as this can cause serious damage to the electronics on either car.
If the jump leads get hot switch off both engines and allow the leads to cool to avoid a possible fire.
Turn off the ignition on both cars and then disconnect the leads carefully in the reverse order to the way that they were connected. Be careful not to touch the clips against each other or against the car bodywork.
Start the car that had the dead battery using its own battery power. If it won't start this could indicate a more serious problem with the charging/ignition system that will need investigating by a professional.