Tilton, NH
On machines without free play code the LAST thing you want to do is drill holes and put in switches... Gross.
On Gottlieb System 1 through System 80 the trick most do is to wire a jumper between the Start buttom and coin switch diodes down in the bottom of the cab. That way very time you hit Start, you apply a credit and instantly debit a credit.
http://www.papinball.com/tips/gottlieb_free_play.html
On most other machines, an insulated switch mounted behind the Credit button or the coin return button and wired across a credit switch works wonders.
On some early solid state Bally/Stern folks have modified firmware, and if you have the means to burn roms, go for it.
