What battery cable to hook up first?

Spray both terminal ends with anti-corrosion solution. Attach and tighten the positive battery cable (Red). Attach and tighten the negative battery cable (Black). Ensure that all cable connections/ hold downs are properly tightened.

Similarly, which terminal do I disconnect first on a car battery?

Determine what size socket you need to loosen the nut on the negative terminal. Always work on the negative terminal before the positive when you disconnect your battery. Grab a socket from your socket kit and hold it near, but not against, the nut on the negative terminal of your battery.

Why do you take off the negative battery cable first?

This is because the chassis of the car is connected to the negative cable. If you started removing the positive cable instead, your wrench could hit the chassis and cause a short (because the chassis is connected to the battery's negative terminal).

Do you hook up the positive or negative first?

If you connect negative terminal first, there are chances are circuit to be shorted while positive terminal is connected. Always while connecting, positive terminal first then negative and the ground (to avoid fuse).
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