still not right.

Depending on what bigtime sparks are you need to solve a short or current draw problem first thing.
Make sure everything is off on the car including a possible interior light.

Not yet connected wires is not going to cause this.

I get little sparks because my stereo has memory settings and has to be connected to full time power.
It's possible the MSD box is drawing power (try disconnecting it's power lead to the battery and try it)

Are your sparks making ANY visible marks on the terminal when it sparks?
If so, you have a fair short to ground or a big amp load for some reason.