You're shorting it somehow........don't get sparks unless the neg and pos are crossed. Check and make sure you didn't somehow get solder across both terminals.

Never work with both ends exposed. Just too many things can go wrong and cause a short. I leave the HS protector on one end until I have the other end soldered, Only then do I remove it and work with it.

I find Deans easier if you'll do the positive 1st - it goes on top and its inside so to speak on females. Then the black is easy. The other way around, its toughter getting the pos in when the neg is already there.