It sounds like either the power supply or earth fed to the gauges is failing. Often an electrical feed can pick up via an alternate power source, if the main feed is interrupted, like via a bulb, resistor, etc, but as soon as the gauges requires more power / amps than the alternate source can provide, it fails.
My suggestion would be to obtain a wiring diagram for your ride and attempt to trace which of the power and earth feeds have failed. It may even be as simple as a blown / corroded fuse terminal. Let us know your progress.