double check next time you're under the hood that all the connections to your coil are good and snug, if they are and your'e still arching, i'd say if you've got your old wires around, slap those on and see if you get the same thing. if so, buy a new set of wires, maybe changing one by one with the bad ones to see if it solves the problem - and if not, return those so you're not out that money...
beyond that, i wouldn't really know, i'm no expert.
but my guess would be the coil.
