Hi Monty, and welcome to the forum.
Check that the Seatalk connection to your cockpit instrument has not become disconnected. The Seatalk cable carries both the data connection as well as the power to illuminate the instrument. If when you switch on, the instrument becomes activated, then it’s possible that the data connection alone is faulty, or the instrument itself is faulty. One way to check would be to switch the two instruments around and see whether your tridata instrument works at the multi position. If it does work there then you have a fault somewhere in your Seatalk system, but make sure that both instruments are fully connected to Seatalk before you try this as the instruments themselves become part of the circuit. If it doesn’t work, then it’s likely your tridata instrument is faulty.
Good luck.