There is no freeplay setting on System 1 games. You can set the replay score to 10.000 and always have credits. Or, add a wire from start button to one of the coin switches, it will then give a credit and start game when you push start. From pinrepair.com:
Modifying the Switch Diode Strip.
This modification and pictures are thanks to PaPinball.com. By far this is the easiest way to add "free play" to a Gottlieb System1 game. Just solder a wire from the coin door credit button wire to any of the coin switch wires. This is done easiest at the diode strip in the bottom cabinet. Make certain that the diode, credit button wire, and coin switch wire are still soldered securely to the diode strip terminal when finished. If soldering is not an option, use a small alligator clip test lead. Now when the coin door start button is pressed, a credit will be incremented, and then decremented (because a game is started.) Now a game can be easily started without the need to open the coin door to trip the coin switches.
Gottlieb System1 Bottom Board Diode Strip Wires:
Credit button wire: Green-White or Brown-Yellow-Yellow
Connect to any of the wires below at the diode terminal strip -
1st coin switch wire: Orange-White or Brown-Red-Red
2nd coin switch wire: Brown-White or Brown-Orange-Orange
To stop awarding credits at high score, turn switch 22 off. And to disable replays, set all 3 replay levels to 0. Switch 10 turns match feature off and switch 11 changes Special award to extra ball. You can also opt to disable credit display, that is done by switch 13.