I thought I'd show what's been taking me so long to get what feels like almost nowhere.
Being of the non electrical type it has taken me a fair amount of puzzling and faffing about trying to get some sort of a plan formulated. Here's what has evolved so far =>
The explanation is as follows
Part A - a big old terminal and distribution thing - is used for the "always live" parts such as the interior light, the horn and side / parking lights.
From this two chunky 6mm^2 cables run down to two 40 Amp in-line fuses that protect two 40 Amp relays (Part C for example) that will be activated by the ignition switch. In this way only a small current will be passed through the ignition switch - the hard work will go through the relays.
Each relay has its own "big old terminal and distribution thing" - Part D and Part E
The light green wires running from Part E power the lower row of fuses (Part F) - whilst the purple wires power the upper fuse row. That simple colour coding helps me trace things slightly more quickly.
The smaller size relays with a "D" for diode on them (the bigger relays are also diode versions used to try and aid electronics I might be running from the power sockets) that sit between the big relays and the fuse box are all rated at 20 Amps (if I remember correctly) and are used for things such as fog lights and horns and headlights and the blower motor etc
I need to group the switching sides of the relays into connectors that will all come from a common feed from the corresponding parts D, E, and A. These wires will be detachable from a new loom section - much like the other connectors that go to the loom sections I've already fitted - so I can remove and change / repair this whole fuse box and relay section away from the rest of the wiring in the car.