The neon high voltage indicator light (Location of light may vary on your unit from photo) operates by induction- that is there is no physical connection of the light bulb in the camera. With the light used in this way, you are assured that if the light is lit, high voltage sufficient for the coronal discharge is present. This also indicates that the high voltage output coil is working properly.
The supplied Ground wire with clip is used to supply an electrical ground to the unit, or opposite polarity to the subject, depending on how you are using your unit.
Caution! High voltage is present in the output wire when the pulse button is depressed. A slight burn can result if you touch the output jack or any bare metal connected to it while it is energized.