Merc 120XR Tach not working

I have a 96 Rinker Jetboat with a Mercury 120XR, I just finished replacing the Stator and Trigger and flywheel due to the magnets coming off on previous owner. I have the boat running pretty good, but also just noticed that the Tach is not wokring. I pulled the dash apart to get to the gauge to verify the connections and to check for voltage and such. I can go across the ground to IGN and I see my voltage, I can go from ground to Send and I can see voltage and it increases as I run the throttle up, but the tach doesn't read.

When the ign is off the tach goes up to about 1000 but when I turn the key to on it drops to 0 and only wobbles as I start the engine, but thats it. I stopped by my local trade shop to pick up a used one for testing and it does the same thing, so I am assuming my gauges are good.

Any thoughts and can I bypass the voltage regulator to get the tach working, or is it best to replace it?? Boat runs good for sitting for over 3 years, just have to finish adjusting the carbs mixture and a slight leak in my fuel system.

do you have a voltmeter in the boat?if not place a voltmeter across the battery terminals...you should read battery output only with the engine not running..start the engine and after it runs a few seconds you should see the voltage has increased above battery output...if it does your charging system is working..
there is a grey wire off the regulator that is your tach feed..if the regulators appears in the prior step to be working then verify that the grey wire has the same voltage on it at the tach...if you voltage says the regulator is not working then you can move the grey wire to one on two wire coming from the stator..they are probably yellow..

you need a voltage wire and a good ground at the tach as well as the feed wire..dint assume some tach that is used from someone else is still good...

I have the voltage at my Grey wire and after running the engine I can watch it increase to 14. something when I run up the throttle, so I know my charging system is good, besides all that was replaced with new parts due to catastrophic failure of the magnets in the flywheel.

I didn't know if these Tach's are different from that of others as I had read they work off Frequency not voltage and this is why you can't just use a VOM to test them. But for continuity reason's I used my VOM to check the wire for connectivity.

Appreciate the feedback. I was going cheap on the isolation and they didn't have new 2" tach's for my dash, so I had to improvise.

voltage regulators and rectifier only charging systems do not filter to a flat line dc...in fact you can flip your meter to ac and read this ripple...these ripple pulses are what the tach needs to measure rpm...that is why the switch in the back needs to be set to the proper setting depending on how many magnets and windings are feeding the regulator..