Final answer:
Before connecting jumper cables during a vehicle jump-start, it is essential to turn off both engines as a safety precaution to prevent electrical surges and potential damage.
Step-by-step explanation:
The instruction to turn off both engines before connecting jumper cables is a safety measure in the context of automotive maintenance, which falls under the category of Engineering.
When handling jumper cables, it is crucial to ensure that both cars involved in the jump-starting process have their engines turned off to prevent electrical surges or sparks that could cause injury or damage to the vehicles' electrical systems.
It is equally important to follow the correct sequence when attaching the cables: connect the positive clamp to the positive terminal of the dead battery first, then the positive clamp to the good battery, followed by the negative clamp to the good battery's negative terminal, and lastly, the negative clamp to an unpainted metal surface on the car with the dead battery, away from the battery itself, to serve as a ground.