[yossarian19]

You've got a current draw. If it's sparking like holy hell, to the point you don't want to hook it up, something is wrong. It's not dangerous, it's just not "right".
12 volts isn't nearly enough to do you any harm - your body's electrical resistance is (in the very worst case) around 2250 ohms. 12 volts / 2250 ohms = not enough to hurt you.
That said - something is consuming power that shouldn't be. Key on? Glovebox light / dome light? Brake switch?
You need to do a "draw" test, and find out where that electricity is going when it leaps from battery to cable.