The switch port is 2 wires in the electrolyte tank, beside each other, on the same level.
When the electrolyte level is lower than the wires level, the outer circuit will open, and red led will be on.
When level is ok, higher than the wires level I mean, the green led will be lighten, and stay on, as long as the electrolyte level is ok.
Update: modified for car battery 12v
