seeking wiring diagram explanation

[cann]

I am very new to the bongo world and trying to follow the wiring diagrams can understand most but cannot figure out eg where the wire shows the colour letters there is an extra letter in brackets this is also seen in the wiring colour chart, can anyone explain this for me please, my aim is to fit a switch to the engine ecu supply.

[g8dhe]

The letter(s) in brackets is the "name" of the wiring loom the collection of wires that are bundled together they also have a printed pattern associated with the name for the physical diagrams;

Most of the bigger looms run between the X plugs where they breakdown into smaller cable runs to individual devices.

[cann]

Thankyou for the explanation, I can now continue with peace of mind to go in the loom to modify. Regards cann.