The engineers wrote it as a very basic description for a mechanic. They did not get into hydraulic circuit design and theory in that write up. Which is why it's full function is not explained. All the mechanic needs to know is that if the light stays on, or it never came on, the problem is that switch.
And that's the limit of your understanding too.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
