Originally Posted by padlin
I believe you connect the black (-) lead last, no idea why.
I believe it's because up to then it doesn't really matter if your wrench hits any metal that's grounded. If you hook up the negative and have a little slip of wrench when working on the positive terminal and it hits ground you'll find out what a bunch of amps look like.
When I was a kid learning how to deal with batteries in aircraft that lesson was impressed on me. Blow a hole in a fuselage and your day will only get worse.