If it looks like the one in the lower left corner of the photo and lights up when you turn it on, it puts the water heater into "electric" mode (on 120V). BE SURE the water heater is full of water before doing that, or you'll get a quick course in replacing the heating element. On your tank monitor panel, there may be a small rocker switch on the right side that says "HEATER." That puts the water heater into propane mode. You can run it on both or either. When the propane is firing, a small LED will light next to the small switch. There is also a black rocker switch on the outside face of the water heater that needs to be in the ON position for the electric to work. Once you turn it on out there, there is no need to turn it off, since the red "light" switch will control it.