The LED indicator lights show the water level in the 13 gallon water tank I built and installed in the dead space inder the van on the driver side adjacent to where the side door step is on the passenger side. I simply drilled holes in the tank wall in a vertical line and installed galvinased maching screws than protrude into the water. Attached wires to each for a ground when the water reaches that level (grounded the water at bottom of tank).