Correct, the Park/Tail and Instrument Panel lamps are usually on the same fuse.
Depending on how it is wired, a bad earth may only affect part of the circuit though.
For example, in a B110, the Instrument Panel Lamps have their own earth as do the front Park Lamps and the rear Park Lamps.
So even though they all get power from the 10A PT fuse, the earth connection for any individual section may be faulty.

I think with a Datsun and many other Jap cars, when dash lights are out this means there is a problem with your tail lights, Bad earth or park lights not working or switch on headlights.