Yamaha Tachometer Erratic

[Jeff5047]

The Yamaha Digital Tach on my 2001 F-115TLRZ started to read erratic this afternoon. The tach will jump high in RPM by 20%-50% every 5 or 6 seconds and then return to normal. No change in load or motor revs accompanies the change on rpm reading. This is ocurring at all engine speeds. I checked the connections under the dash and have not found anything which could explain what is going on. Looking for troubleshooting suggestions.

[boats.net]

That is probably a bad tach, try a new tach.

[Jeff5047]

Any way to tell its a bad tach before spending $350 on a new tach?

[boats.net]

You can connect a AC voltmeter to green wire at tach to see if signal voltage stays steady.