I assume you want to read the voltage going to the landing light bulb itself, and you don't have a voltage anywhere that you know of that just goes DC high or low when the lights are on or off?
If that is true, I think you can get what you want, but you need to mess with the sensor file.
The sensor file has the ability to add filtering and the EMS samples at 16Hz. So if your lights go on and off every second, and you add a 4 second filter, you should have a output that is pretty stable around 2.5V when they are on, but still zero when they are off. If you set your contact to be "on" at more than 0.5V or so, I think it might work. Note that it will take a few seconds after turning on or off to see the effect on the EMS since you need to wait for the filter to react.
Make sense, or do you need some more help?