You'll need to look at the switches and circuits that send power to the score motor. Find the score motor icon on the schematic and work back through all the switches that send power to the score motor. Make sure those switches are clean and adjusted properly. Either one or more switches are mis-adjusted and they're sending power to the score motor, or a relay coil is energizing at the wrong time...

http://photos.app.goo.gl/yCc8acg7ki1KwTlH2

First check the coin chute switches to make sure they are open. Then make sure the bonus unit is resetting completely. Also, make sure all the score reels are resetting fully to zero...

Here are the switches that send power to the score motor:

Score motor switch A-1 - green wire and grey/black wire
#1 start relay switch - green wire and grey/black wire
Anti-cheat relay switch - green wire and grey/black wire
Ball count relay switch - green wire and grey/black wire
Out hole relay switch - green wire and grey/black wire
Credit reset relay switch - green wire and grey/black wire
Bonus collect relay switch - green wire and grey/black wire
Top hole relay switch - green wire and grey/black wire
25 cent credit relay switch - green wire and grey/black wire
5 cent relay switch - green wire and grey/black wire

Check these "primary" switches to make sure they are clean and adjusted properly.