Find the wires that goes to the credit light in the apron. You should be able to pick it up at one of the driver board connectors in the back box (yellow-purple and red-gray wires). That way the start button would only be lit when there is actual credit on the machine. You could even use a flashing LED and the machine would look all modern. Naturally you would need to use a diode at the lamp socket since this is a matrix lamp.