Always connect the negative last.  That way there's no circuit if you happen to short the positive to the body of the bike.  And, the negative won't spark cause it connects to the body of the bike.

That big ol' spark will sure wake you up quick.

IF there's a current draw the negative will spark when it's connected,size of spark depends on how much draw, If not,neither side will spark,Provided no one causes one accidentally. It's just bad practice to connect the positive side first. Sparks near the battery are seriously bad practice. I was using a grinder on the header,mounting the Supertrap,when sparks got close to the battery vent tube under the bike.. Sounded like a 22went off. Time for a new battery..A battery explosion can cause Real injuries. If you Suspect that the wiring is causing a draw, I suggest connecting a test light and see. Don't be hooking up a battery charger that's already on. Hook it up,plug it in.