For what its worth, my copy of the honda service manual says "ground temperature sensor wire and turn on ignition..........Disconnect the thermosensor wire when gauge moves fully to H..................Caution: Do not ground thermosensor wire for more than 5 seconds to prevent damage to the gauge".

If true, no sensor should give no gauge reading. If you have a gauge reading without a sensor, an earth may be missing somewhere.

Rick O grounding kit :) or DIY the same setup. Worked a treat on my track bike.