If you have the Whale water system I suggest you search for the various posts on this forum. I'm not sure what water/heating system you have but the supplies will be fused in the Sargent PSU.
There are inline connectors in both of those looms that are taped in but can be a cause of problems. The waste and fresh water level indication looms connect to the psu as well. The split charge relay is part of the main Sargent PSU.
Three fused input feeds are in the fuse box in door side panel under the drivers seat and the circuit fuses are on the outside of the EM50. That is where the vehicle battery is connected to the habitation circuitry and it houses the fridge and step relays, provides 12v feed for the fridge and reversing camera and has the interface to the central locking. Under the drivers seat is the Sargent EM50 that is the interface between the van and habitation electrics. There is a switch to disconnect the vehicle battery if the van is stored for a long time - see Mercedes handbook. Vehicle battery and a useful toolkit under the carpet in front of the passenger seat. Leisure Battery with its fuse and a temperature sensor under the front passenger seat. Unless the Mercedes install has changed you should find:
