I discovered that there is a positive and ground wire running through the bottom of the rear overhead storage in our 2011 3670 Big Horn. I suspect your Landmark will have the same. We put the illuminated switch in as you describe. We installed the Voyager model WVOS511 and are working with the manufacturer to get it to get it to communicate with the monitor 100% of the time. If there is nothing close for the signal from the camera to reflect off of, we lose the signal. The signal will not penetrate through the unit. On a positive note, their tech support is working with us to find a solution. I hope your experience is better.