Not that it is a fix, but out of the 10 or so tractors of various brands I've operated over the years, only two didn't occasionally take a few smacks with the palm of your hand on the dash to get it working. I think the needle just gets stuck from humidity and condensation and just needs a little shock to work free.
If a few taps of the hand don't get it working, I'd check out the wiring where it passes through to the engine. That is a common wear point for all tractors.
I've also seen cases of connections becoming oxidized inside of the various plugs and connectors. Disconnect the various connectors and inspect the terminals for any sign of oxidation. Spray them out with electronics cleaner and plug them back in. If you come across an oxidized connector, clean it up really good and be sure to use some antioxidant spray before reconnecting.