Does your fresh water level display show Empty, 25%, 50%, 75% and Full?
If so it needs a 5 wire harness as shown on the Sargent Electrical website https://sargentltd.co.uk/shop/product/ec155-fresh-water-harness/342
And here are the 5 studs to go with the harness https://sargentltd.co.uk/shop/product/ec51-fresh-water-studs-and-screws/136
I'm guessing your tank is insulated so you need to find the remaining sensors and clean them.
Keith.