The tach input is from your alternator. A pink wire in the altenator harness is the signal output going to the tach. My tach sticks sometimes on my tractor and I have to tap the face of the instrument panel to get it going again. But it has never failed once it is working.
The instrument panel has a fuel gage, the tach, and a temperature gage that are all individually replaceable. You have to take the instrument panel module out of the tractor and disassemble it. There are two tests listed in the repair manual and both are resistance checks with an ohmeter on the removed tach. I can give you those tests if you want to do this yourself, but your dealer should also be able to check this for you if you don't feel confident.
Do your headlights work? Fuse #4 is the headlight and instrument panel fuse. I would remove the instrument panel and check fuse #4 under the panel. I would then remove and reconnect the connector to the inst. panel and check the connection of the the pink wire on the alternator. Put everything back together and check one last time before taking anything apart in case it was a bad connection.
Let me know if you need more assistance in removing the tach. I think I have a thread here with some pictures that might help. I'll see if I can find it.
EDIT: Here's the link with some photos. Even though I am replacing the temperature gage, the tach is right beside it and comes out in a similar fashion.
Instrument Panel Surgery
BTW: Rich, welcome to TBN and the New Holland forum.
