Re: tachometer malfunction!
Still unclear -- but yes, the tach should move from zero to whatever wide open throttle RPM is. Normal tach operation goes like this:
1). Key on (engine not started) tach should read Zero. The tach needle, with the engine off, may stay anywhere on the dial -- that's normal.
2). Engine running, should register idle RPM 650 RPM or so.
3). Wide open throttle should be in the 5500 - 6000 RPM range.
It would help if you checked those three situations and let us know what's really happening. There is a dial on the back of the tach. Check the setting of that dial. Note its current position, then rotate it back and forth stopping at the same setting. That's the calibration dial. Sometimes they can become intermittent and give erroneous readings.
I'm really "reaching" here but If the tach reads at the high end of the scale with the key on (engine not running) I'd suspect the ground and +12V lines are reversed or the sense line is shorted to +12V or some similar scenario. Just because the connections are tight does not mean the right wire is on the right terminal and make sure a wire has not spun around and is contacting another terminal.. Since the sense line comes from the regulator/rectifier it may be that component is bad even though the charging system is working as it should. If you have a voltmeter, what does it read at idle and about 2000 RPM? If it reads 12.6V or a little above at idle and 14.5 volts or so at 2000 the charging system is working. If voltage stays the same, its not working and that may be the cause of the tach malfunction. It the tach reads zero with the key on (engine not started) but goes goofy after the engine starts, I'd suspect an incorrect sense line connection or a problem in the wire harness between the engine and the tach. It is also possible that the sense line is picking interference from some source on the boat such as a locator but that would really be weird. Lastly, it may just be a bad tach.
