On the main light switch(or dimmer) will be a Light Blue wire with a Red stripe, that's the wire that sends out voltage to all the instrument lights.
It often comes out of the main light switch(or dimmer) and goes to the fuse panel, through a 10amp fuse and then out to the light bulbs.
The reason for this is because a short in one of these light wires could blow the main head light fuse leaving you "in the dark" while driving.
Parking lights can also share a fuse with dash lights, so make sure Parking lights are working
So there is often two fuses to check if dash lights are not working, in cab fuse panel
The dash lights get power when main light switch is on AND when DIMMER is turned up.
When you turn dimmer all the way up you should feel a click from that **** and the dome light should come on.
If that is not happening then could be the main light switch needs to be replaced, the DIMMER section is worn out, which can happen at 28 years old.
To by-pass the switch you need to add another switch.
Best method would be to pull out Main Light switch to get access to the wiring.
Cut the Light Blue wire with a Red stripe leaving enough to reconnect it later.
Use a long jumper wire from Battery positive terminal connect it to the Light Blue wire going OUT to the lights, just to test if the lights work or if there is a problem farther on in the circuit.
If lights work with 12volts applied then................
There should be a Yellow wire with Black stripe on the main light switch, you need to get power from that wire using a splice, don't cut it/disconnect it.
Run that splice to a switch, I would add a 10amp fuse on this wire.
Connect the Light Blue wire to other side of that new switch.
Switch needs to be rated for 20amps at 12volts