If your vehicle is showing dashboard instrument cluster lights are completely dark, here are the most likely causes and the parts you'll need to fix each one.
The interior illumination dimmer switch was accidentally bumped or turned all the way down. This is extremely common after cleaning the interior of the car.
A blown fuse has cut power to the instrument panel lights. This is frequently caused by a shorted illumination wire during an aftermarket radio installation, or a short in the exterior tail light circuit.
On older vehicles without LED clusters, the incandescent bulbs behind the gauges burn out over time. While they usually fail one by one, multiple failures can leave the cluster completely dark.
The main headlamp switch, which triggers the dashboard illumination circuit when the headlights are turned on, has failed internally and is not sending power to the dash.
In modern vehicles, the Body Control Module manages interior lighting and dimming. A failure in this module or the cluster's internal circuit board can cause a total loss of backlighting.