You may have a loose connection on the back of one of the instruments or possibly a short or bad connection leading to them.
When I took the dash apart on my '78 Shadow II I was surprised to find that the odometer was entirely electric and used slide-on electrical connections. These do not necessarily age well.
It appears (though I'm going from memory, so don't count on this) that a number of the instruments are running in series as far as getting power goes. If you lose power at the first in the series, others will "go out" too. I do believe that the odometer and the "quad gauge" that includes the battery and oil pressure share a connection.