On the coin stepper there is a contact that should open after the fourth player is selected.
A lot of times the pin is on the wrong side of the contact preventing it to reset properly.
Other thing could be a broken wire on the reset coil or a contact on the reset relay.

Clean the wiper and the contacts, turn the spring tighter (one turn!).
Contact on the coin should open when the fourth player is selected.

For free play: machine off, close the two contacts that open when the credit is on the blank (0).