Switches where the same thing happens when you switch them are no use.
The switch needs to do something useful in two different sets of circumstances for it to be useful.
The simplest living organism is full of switches and control systems.
The biochemical pathways shown here (you can click on the first image to see parts of the diagram more clearly) have elaborate control systems that operate at different levels.
The biochemical switch that controls the two possible lifestyles of the virus called Bacteriophage Lambda has been studied in great detail it was this little switch that convinced me (way back in 1986- see here) that there was a real case for an intelligent designer.
One of the snazzy molecules involved in a DNA/protein switch: