I also discovered that my tractor has electroluminescent gauges. Rather than being illuminated by traditional light bulbs, they are illuminated by electroluminescence. It's difficult to explain how it works, so here is a link for a better description.
Electroluminescence - Wikipedia, the free encyclopedia
All of the gauges work, except for the generator (amps) and water temperature. When illuminated, they have a soft green glow that looks really cool at night. However, I suspect that finding replacement OEM gauges (new or used) of the same type may be difficult and/or expensive, so I am considering the possibility of replacing them all with new ones. However, I'd like to have accurate hours showing on the tach so that could create a complication if I decide to replace them all. I'll try to take a picture of one of them later.