The real problems come with networking the switches. Instead of old fashioned hard wiring of switches, we now use Ethernet switches and data lines linked to processors to turn switches on or off using aliases. It's like machines now make millions of phone calls to each other 100 times a second. These calls are "scan times" in a program. Certain conditions or requirements cause stuff to turn on or off based on the program. I can have a part go bad in a machine and reassign the tag that sends or receives the phone calls to another alias switch or component function with the click of a mouse and a few cut and pastes. No change in wires needed.
The now bigger problem is when I insert a line of code in the program which does not include a reset or a jump instruction. Now the 1000 times a second scan time comes to a screeching halt. No more machines calling other machines. Everything stops.
I can make an elevator in a building run using an Ethernet linked refrigerator door light bulb. Every time the refrigerator door opens the elevator will stop. The havoc I can create is endless! The solutions I can create when an important machine stops are also endless. It's a matter of integrity of the person doing the work.
Now you understand voter fraud in machines. I can use each vote triggered for candidate A to write a bit to a machine in Hoboken and at the top of each hour transfer that block to candidate B in Boise Idaho. I can do it all using any system which is connected to a shared network and some disclosed IP addresses in my system targeted.
That all just gave me a spasm in my brain. :)