There aren't any special instructions. Did you install the 6 digit or 7 digit displays? Ball in Play and Match appear in the same segments (The last 2), so maybe you have MATCH turned off? Also, if you're using an Altek MPU have you set it for free play? Putting the early Bally SS machines on Free Play requires turning off the credit display.
Also, if you are using all new LED displays, you don't need the High Voltage. You should remove the small High Voltage fuse from the Solenoid Driver Board (With the machine unplugged, of course!)