Goood morning, Jeff. This is Ed.
Like most electrical devices these days, instrument cluster backlighting may have become a bit more complicated than it needed to be. But with that said, I think we should be able to narrow the problem down to a couple of components or power inputs.
Your cluster uses what is described as a single electro-luminescent lamp that accomplishes backlighting, instead of several individual bulbs or LEDs. It uses a 12v DC input to a transformer onboard the cluster that steps power up to 80 volts AC, so if either the lamp or the transformer go out... they all go out.
Input voltage to the cluster comes from four sources, but it's not specified which one is tied to your cluster backlighting. Since the fuses are located at opposite ends of the car, I'll make mention of them, even though you've likely been through that already.
IN THE TRUNK, you'll find Fuses 14 (10A) and Fuse Breaker #1 to be hot all the time. Fuse 29 (5A) is powered up with the key in the RUN position, so it's not likely the illumination circuit.
UNDER THE HOOD, you have only Fuse 5 (25A) to check and it's also a B+ (always hot) source.
Next, do you see background illumination on other panel components, like HVAC or switches when the headlamps are turned on? If nothing at all lights up in the dash, or if your VFD -- sources like the odometer -- fail to dim and be controlled by the dimmer wheel when the lights are turned on, I'd expect that the dimmer switch on your headlamp control switch unit has failed. A single input to the cluster is sent from the dimmer, then recognized and relayed to other systems for control of switch backlighting outside of the cluster unit. If you find backlighting or dimming of radio VFD info to occur, it positively shows that the dimming signal is at least being received by the cluster.
Check these few things out and let me know what you find, Jeff. It's my feeling that your headlamp switch is the problem source, but we'll know more shortly.