In the UK it’s very hard to get circuit diagrams or repair manuals. I get many emails from people looking for repair manuals and wiring diagrams for white goods appliances, but they are only available to the trade. Even then they are commonly only available by opening a trade account, paying a subscription and logging online into a manufacturer’s secure technical support web site. Another common way the trade can have access to them is by subscribing to them on DVD, which isn’t cheap, and needs renewing every several months or so. Gone are the days when we used to buy the wiring diagrams and repair manuals in printed form.
Providing water level indication eg, by using a dishwasher pressure switch to activate LEDs or lights to indicate the water level in a tank. By using two dishwasher switches and adjusting their individual set-points, it's easy to have six levels indicated. However, you'll need a lot of wires to connect the switches to your display.