The ground doesn't have to be at the battery. Could be anywhere there is a good ground.
Example:
Take your pencil and follow the path to complete the journey from the battery Positive to the Negative.
It has to be a full circle for the lamp to light.
That path your pencil followed is what the light is testing. That's it. No more, no less.
Example:
Take your pencil and follow the path to complete the journey from the battery Positive to the Negative.
It has to be a full circle for the lamp to light.
That path your pencil followed is what the light is testing. That's it. No more, no less.