After driving the amazing new Connex Class 375 on London - Brighton, I then decided to test a non-electrified an to my shock the locomotive which was on the "locomotive selection" list was the Connex 375. So I thought, "MSTS will crash when it loads the route because it will relise that you can't run a 3rd rail train on a non-electrified route."
But...

Notice how there is no 3rd Rail in FineScale and I assure you in RE I have NOT electrified the line with wires set to a high hight or even put it in 3rd rail.