Another easy way to set up a EM machine for free play is to move the wires
from the coin-detect switch to the start button. The "coin detect switch" is
the switch the coin will fall on when you put one in. Make sure you have
the right switch, when pushing it by hand the machine must start immediately,
a second press will give a second player. Loosen these wires and also loosen
the wires connecting the start button (the one you press if you have credits
to start a game). Solder the wires from the coin to the start button,
isolate the other ones and voila, there it is.