# How short circuit is made when connecting negative cable first when jumping start the vehicle

When Jumping start, I understand that I need to connect the positive terminal first due to the safety reason. And also if I connect negative terminal first and touching the body of the vehicle with the wrench by accidentally, I might damage the battery due to making a short circuit. And could you explain how the short circuit is created?

• The body of the vehicle is connected to the negative side of the battery. Some old cars use a positive-ground system, though, where the positive side of the battery is connected to the chassis. – Hearth Oct 27 '18 at 16:49
• At least for US cars that'd have to be a really old car. I think the last positive ground Fords were produced in the 1950's. – TimWescott Oct 27 '18 at 16:52
• The reason for connecting the cable to the chassis rather than the battery is a spark could cause an explosion. Lead acid batteries give off hydrogen. I know this to be true. My cousin's battery blew up in his face while connecting the cables. . – Misunderstood Oct 27 '18 at 19:07

• Could you please make it a little clearer? However, if you had already connected the negative jump-lead first on both sides, or just one? , then you would short out the battery on one vehicle which one? if you accidentally touched the positive jump-lead against the chassis. so the positive jump-lead is already connected on one side, and touches the chassis on the other side? – Lodovik Jan 30 '19 at 21:38