I recommend trying out funkboxing’s FastSPI2 effects as great examples of using the FastSPI2 library. You will need to use the line LEDS.addLeds<WS2812, 13, GRB>(leds, NUM_LEDS); to properly initialize the code.
Test the LEDs, and seal it all up with electrical tape
Reinstall lightbars and brakets, reinstall the front cover, and reconnect the wires.
See more about these fun little LEDs here. The case front has 4 LEDs in it, so each side has a top and a bottom LED, making some interesting colors in the middle. Even more interesting, the little airbubbles in the plastic lightbars glow two colors: one for the top, and one for the bottom.