2001 F115 tach sender

I'm having problen, I guess, with not getting signal for Tachometer (Yamaha 6Y7-83540-80-00). It stays on 0 RPM. I just checked to hook up another Tachometer( Teleflex Amega) and it was just the same. What should be reading on green wire, how to check it, and where is the wire comming out from the engine. Thank You for advice.

[boats.net]

Should get AC voltage reading as engine rev's up, gets signal from ECU.

If there is no AC voltage, do I need a new ECU?

[boats.net]

Could be ECU or wiring harness.

Thank you, I'll go through harness, and let you know what happened.