Mine isn’t working, likely because the light source is fried.
I'm not familiar with the '74 and all of its uniqueness, so I cannot say what's there or how it should work. However I will pass along some general info that might help.
Apparently there were at least two types of rheostats used on the X; one will dim LED's but the other will not. There are some threads that discuss this in detail. However I don't know if the one in a '74 is like either of these (it looks smaller to me?).
I'd suggest removing the center console (control panel) and inspecting the dash illumination system that Don described:
The bulb is mounted on the tunnel behind about where the lighter is. It has a metal cover over the bulb with a fiber going to each switch. Check to be sure the socket has a good ground as well as power.
I wasn't sure that the '74 used fiber optics, but now that he has verified that...
The way the fiber optic system works is there is one light source (a single bulb) in the holder behind the console (as Don described). From there the "light waves" are carried by fiber optic lines (looks like fishing lines) to each of the destinations. I don't know exactly where on a '74 those destinations are; just the center controls or also all of the gauges, etc?
@dllubin can tell us that. But if that single light bulb is burned out, or the fiber optic assembly (bundle of fishing wires) has come loose from it, then no light can get transmitted to all of the sources. So all of your problems may be a single simple fix. But that bulb is where a LED can be swapped in to further improve the system (it will provide much more light waves into all of the fiber optic lines).
While in there you can also clean up all of the electrical connections. And you can find out if your particular rheostat will control a LED bulb. If not then maybe revert back to a new "standard type" bulb, or bypass the rheostat (but that may be TOO bright). Because as
@kmead said it doesn't look like you can use one of the newer style rheostats on your '74.
Once you have sorted out the fiber optic system, you may find only one or two places that should illuminate but still don't. That is likely because the
other end of the fiber optic has come loose from its holder. They have a little receptacle that holds the 'fishing line' up to the back of what should light up. And those can come out of place, not allowing the light to pass.