When changing a car battery, why do you disconnect the negative first and then the positive, and vice versa when putting a new battery in? What will happen if you do it the opposite way?
In: Engineering
The negative terminal is connected to the entire frame of the car, allowing you to use any metal point inside the car as a battery negative connection point. This means you could accidentally touch the positive battery terminal with a part of the car with your tools and cause a short circuit of epic proportions.
Disconnect the negative terminal first to break this connection, and now the only way to make a short circuit is to touch both battery terminals together which is much less likely to be done accidentally.
(There are a variety of reasons to make the entire car frame effectively the battery negative terminal, but that’s a story for another day)
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