You say that when you turn on one switch, the other switch lights up. So are you saying that the led in the panel switch is
lighting up or is the actual light in the mast
lighting? If it is just the other panel switch and not the actual light, then you have some low
current bleed probably at the panel. It doesn't take much
current to light one of those lights in the switch. Are the two switches right next to each other? I would start troubleshooting by measuring voltage at the back of each switch with a multimeter when you turn each switch on and off, but only if you are familiar with DC troubleshooting. If you are plugged into
shore power, unplug it before playing around at the back of your panel.