Tachometer not working on Yanmar 3YM20

[DragonflyBob]

After a 4 month layup in the boatyard, we launched our Dragonfly 32 tri a couple of weeks ago. Work on the engine included changing the sail drive bottom seal (7 years old), changing engine and drive oils as well as engine oil and fuel filters, cleaning sea water intake filter and hoses, and changing engine coolant. The engine started fine and is running just great with the exception that our tachometer is not working.

I want to believe this is something simple and that while the mechanics were working on the engine, they might have bumped a connection loose. I removed the main engine control panel to check the back side of the tachometer and the connections looked clean and were tight. I'm not sure where on the engine the sender for the tachometer is located. I could not find anything in the Yanmar manual about its location.

Anyone with similar experience on how to troubleshoot and find the critical connection points?

Thanks!

[SY Harmony]

Which engine?

[Be Free]

The tach should its signal from the W terminal on the alternator.