The reason I am using 24V for the switch voltage is that we are using the original aircraft enunciator / switch that is already installed in the panel. It has a single source of 24V to the switch/enunciator that drives the light and the power for the switched function.
We want to use an arduino to drive all of the lights/switches so we can write a program that will allow us to shoot a scene with the proper actions leading to proper light display. For example, warning lights start flashing and they flip a switch and they stop. Or show the landing gear lights down except one is flashing red, etc...
This is a much newer example: Link to example enunciator
Thanks for all your help, you guys are great!