Such here power supply unit cover. The comb is made that it was easier to adjust a cover to power supply unit if your printer distorts the sizes. I hadn't to take a file(coarse) in hand). A LED of 5 mm, color any, on your taste. It is possible to unsolder a LED from power supply unit and to carry out, on wires on the front panel. If to solder there is no desire, it is possible to take a LED and to fasten 12 volts to a receptacle of power supply unit, observing the POLARITY! To a LED the resistor which is switched on sequentially is necessary. The nominal of the resistor depends on LED current, is complete of any calculators of value of resistance for LEDs. It isn't necessary to drill anything, all screws twist in the existing holes in the casing, power supply unit. Mm M3x6 screws. And two screws, with M4 (it is possible also for M3) nut for fixing of a network receptacle. Perhaps holes in a cover should be reamed under diameter of your wires.
P.S. I had a network receptacle, without light indication therefore I brought a LED to the front panel