The Monitor probe is inserted through a 1/8"" diameter hole drilled through the cover over the center battery cell. An "O" ring around the probe shaft is included to seal the installation. A 1/8" hole is drilled through the strap of the adjacent cell on the side towards the battery negative post and the black probe wire is attached using the stainless screw provided. The red wire is similarly attached to the outboard strap of the cell on the opposite side.

The green LED shows when there is sufficient water in the cell, which is a good indication of the water level in the entire battery.

Other probes have a flashing blue LED (Alert) or a flashing red LED (Alarm) or a combination of green (monitor) and red (alarm).