change your switches around. try swapping the attack and jump button wiring going to the switches for the buttons. if jump works after doing the switch, and attack has this problem, then it's a bad switch OR it's not a problem with your input wiring, but rather the ground wiring, sometimes quick disconnect terminals can fray off the wiring and create an intermittent input. best bet to eliminate any intermittent wiring problems is to just solder the wiring to the terminals direct, but as outlined in the first part, if it's a bad switch it won't make a difference. as a last ditch though, try popping the switch out of the button and check it over to see if it's gummed up with pop or something -- in a pinch you can clean this up with windex and a toothbrush or paper towel, but let it dry first.
if the original problem with jump carries over to the attack switch, then it's a problem with your wiring, which can be narrowed down by what I said before. if you solder the wiring direct to known good switches and the problem persists, then you have to dig deeper into the actual input wire for jump. you didn't specify which player this was for. if it's for player 1 or 2, it will be in the JAMMA wiring .. if it's for player 3 or 4, then it will be in the Konami Player 3/4 harness. inspect wires in this case for stripped open insulators (see: wires that got smashed and cut open). if you find a break in the wire you can fix it easily by cutting out the affected portion, stripping each end by about an inch, and then intertwining the wires so that the wire is straight and running solder over the exposed wiring. do not twist them as this can lead to a later break (I did this for years, don't you do it too.

) then you can wrap it in electrical tape, this is crucial.
I think that encompasses mostly everything about buttons and wires. if that doesn't solve the problem, then I don't know what else.
so... dig deeper. and good luck.
