Milk Jug toss uses inferred sensors to detect the balls. Each sensor has a red indicator LED that tells you the state of the optics. When the game is in attract mode it will always be flashing, when the game is coined up the LED will go dark, when the sensor is blocked the led will light be solid on. You can use a digital multi meter to test the sensor signal lines for proper operation. When referenced to ground the sensor signal will be 5vdc and go to 0 when blocked. The enable signal when referenced to 12v will pulse high and low (in unison with the red led). The white led signal when referenced to 12v will go high when the signal is present.