The next prototype is finished.
It is the 12V junction box with One Wire Bus to connect up to 5 valve control boxes and an additional One Wire Bus junction box for additional temperature sensors.

All my connections and signal distributions will be done this way, like Lego blocks. At the end there will be only straight connections between these blocks. Cable harnesses will be pre-made before I connect everything up in the van.

One thread at the moment deals with robotics and automation. There are so many more aspects in building a van than just building a chassis or a body with different floor plans. Electrical installation in many new vans is still very archaic. Individually connected components with home made distribution boards (12V) and amateurish routed and crimped connections. No wiring diagrams, no routing plans, no schematics, no detailed specifications of components and cabling.

Once I have done one of each required blocks in a subsystem I will connect them up with maximum length cables between these boxes and will test the subsystem if all signals work reliably with that cable length.

For example for my tank control I need 2 of these junction boxes for 9 valve control boxes, and two junction boxes for the tank senders. One tank sender box and 5 valve controllers are connected to one microprocessor handling the valves and the tank senders. Two of these subsystems control the 10 tanks. One other of the same identical subsystem is controlling the rear heating circuits. Designing it this way I can reduce the number of different components and reduce the number of spares I make.

The same concept applies to all the other signal types. Re-using tested subsystems for different components at different locations that not all signals have to be wired back to one place. Distributed processing reduces the number of cables required.
If component locations are known and cable harnesses can be pro-configured that they can be custom made and the final installation only requires connecting the plugs. This is one aspect of automation and is already worth it in my single unit build.

Here is the block diagram for the valve control subsystem. This is going to handle 5 tanks. Two of these are required for 9/10 tanks. The diesel tank has no motorised inlet/outlet valve, only a tank sender.

Valve_Control_Subsystem

Below is the link to the page describing the valve control unit in my internal wiki. The links will not work, because I only loaded this page and not all the others. I keep the links for the component sources (Ebay, Ali Express) for quick reordering when I have the final quantities.
Like this page I document all components and parts used. This development wiki contains everything to rebuild the system if required.

http://teutanic.com.au/valve_control_box.html

If you are interested to get access to my development wiki you can contact me with a PM and I can give you a password, however I need to know who you are and what you your interest is in the site.