Tachometer not working

[realjet]

I have a 2000 Godfrey Sanpan with a 115 HP Yamaha 4 stroke engine. The tach and speedometer aren't working. They do move when the key is turned on and then goes back to zero, so they're not stuck.) The gas gauge and voltmeter work. I'd like to get the tach working (I'm not concerned about the speedometer). I've enclosed some pictures. Any ideas where to start?