I see a lot of damage to ignition systems and computers due to incorrect jump start procedure . You cannot see electricity but it travels in a wave format . Imagine an ocean swell the wave motion is the same as electricity . When you jump start a vehicle or have your vehicle jump started , the wave pattern can jump , like a tidal wave , this wave can damage your computer and ignition system and in most cases are very expensive to replace . Most breakdown patrols have what they call a ' spiking device ' attached to the positive and negitive battery terminals , some jump start leads have this spiking device installed . The spiking device keeps the electricity flowing as a wave and cancels out any tidal wave or sudden surge of power . If your not sure , call a mechanic to start your vechile .