Dishwashers use pressure switches that are similar to those used in washing machines. However, instead of having one switching point, they have multiple levels. For example, a two-position switch may switch at 10cm and 15cm of water, while a three-position switch may trip at 15cm, 25cm and 35cm of water.
Another issue is that any wiring diagram or schematic is subject to copyright so no one should be publishing them on the Internet anyway. As far as I know there are no official repair manuals and schematics for UK washing machines and other appliances readily available.