Hi Graham
The item below the Battery Tray is a Mega fuse for the Amplifier in the boot. It will be connected to Battery 12V . The Power distribution box is the 6 way item just in front of the Battery tray mounts. The new fuse boxes get +12V battery live from here as does the Amplifier. This stops the battery clamp looking like a Christmas tree of connections.
I still have the OE Fuse Box (a NOS item without burnt connectors or heat damaged internal wires). It no longer powers the fans.
My new fuse boxes support the FI Coils, Injectors, Drive by Wire Throttle, ECU power, HP Fuel Pump, Cruise Control, Shift Light, Starter Motor (protecting the OE switch), Accusump, ECU Fault light, Wipers top speed, Brake Lights (protect switch & signal ECU), Fans on lights and 2 x spare relay switch power.
For the symbols they come in sheets from either Pole Volt or Vehicle Wiring Products / eBay for labeling switches. I also used a Dymo label gun white on clear tapes.
The Fuse box /Relay boxes are modular click together items. I considered micro relays then realized with the gauge of wires I am using they would be a nightmare to wire.
A lot of head scratching went into where to put the fuse boxes and how to get the wires in and out of the cabin. I definitely hated drilling for the Rivnuts. NB I dip the Rivnuts in Dinitrol before fitting for a bit more peace of mind on rust.
Other people's cars always look cleaner to me because I know where all the mistakes are!
Eric