We will need:
switch (they must have 3 legs, and the switch must have 3 positions). switch (type of key, according to DESIRE). 4 blue LEDs and 5 red. 4 red LEDs. 11 resistors 750 Ohms. Wires. Shrink tube or super glue. Soldering iron and accessories. Front plug. 3 splitters for power supply.
LED characteristics: Voltage = 1.5 V, Current = 0.015 A.
From here we calculate the required resistance for incoming 12 V:
Resistance = (Mains voltage - LED voltage) / LED current strengths, i.e.: R = (12 V - 1.5 V) / 0.015 A = 700 Ohms or the closest value that can be reached, 750 Ohms
Let's start by taking the front cover ....
.... and drill holes in it for switches and LEDs.
And we screw all this stuff into a stub.
Now we turn all this stuff over to the other side, it is better to tighten the plug in a vice, otherwise it will crawl around the table during soldering.
We solder everything here approximately according to such a scheme, or as you need.
We check the operation - when the switch is brought out of the neutral position, one LED should light up.
We build in the case. And we manage what we wanted :-))
The second option: You can do with one row of LEDs and switches without a neutral position:
Here is a diagram: