Quoted from Ronkz650:
How would 6v burn like a spark plug across a gap?
Oh, it'll definitely happen. In my younger and much more inexperienced years I overfused the GI circuit of my TZ and discovered this. Reaction time upon noticing smoke streaming from under the right slingshot was about 3-4 seconds.
Pulled up the playfield after my heart rate went down to normal and fired it up (not literally) for a couple seconds to see what I could see, and indeed there were tiny sparks in the bottom of the GI socket. I suspect if it were DC rather than AC, a constant arc would have been easy to create.
(The game was fine BTW, and now has the proper fuse and a new socket.)