EM games do not have a free play setting. But converting them to free play is pretty easy and usually just involves soldering a jumper wire or bending a contact.
For EM games, there is a paid game counter (or free game wheel) in the backbox. If the number of games is 1 or above, a switch is closed. If that number is zero, then a switch opens.
The first image is a Gottlieb Play Ball. In the photo, there are zero games on the free game wheel and the switch is open. Second image shows when one game is on the reel, the switch closes. In this free play setup, a wire jumper was soldered on the switch (see yellow – red wire) so that the switch acts closed with zero games on the wheel.
In the third picture, there are zero games on the free play wheel on a Williams Grand Prix. The arm pushes down and the switch should open. But the top contact has been bent down so that the switch makes contact. This allows free play when there are zero games present.
Some people enable free play by clipping the wire to the solenoid that removes games as play is started. This will work for free play, but we do not like this technique since the free play wheel will eventually move up to the highest number of games and stay there. The technique above retains the normal motion of the free play wheel, while still enabling games with zero on the wheel.