Tachometer - Faria wiring connections?

Tachometer on my Glastron GS249 with Volvo 5.7 GS did work, but stopped working after I did some engine tune up...
Bought and installed new Faria tach - but no needle movement.
Only wiring diagram, from Glastron just shows gray wire to engine harness.
Traced what I think is the 'correct' gray wire with a round connecter and found that it is not connected to anything.
Any suggestions?
Thanks

Original tach in your boat likely had a +12 V lead, a ground lead and a lead back to the engine (usually gray). You could also have a separate lead for the internal light. You should have been able to just connect your new tach to the like wires from the old tach with the three originally mentioned wires per above and have it work.

Thank you for your reply. I did hook up the wires to the new tach exactly as they came off the original - which had suddenly stopped working after my doing some work on the engine.
It is my belief that I have inadvertently 'un-attached' the 'sending' wire to the tach. And, I do not know why there would be a wire with a full circle connector near the engine coil going no where.
As mentioned, I have a loose gray wire coming out of an engine wiring harness that goes/attaches no where.

re: " I do not know why there would be a wire with a full circle connector near the engine coil going no where."

That is the wire that goes to the tach. It attaches to the coil. The coil has three connections:
1) The big wire on the top that goes to the top of the distributor
2) A wire that goes to the +12V when the ignition is on
3) A thin wire that goes to either the distributor and/or the ignition electronic module.

Apparently you disturbed this wire when you did some work on your engine. Reattach it to the coil (it should reach nicely) per #3 above. The coil contacts of interest (#2 & #3) are vertical screws with nuts on them that the "full circle connector connector" will just fit on.