Tacho or regulator or Magneto problem?

[ChrisXP]

I have a 93-94 XP Sea-Doo. The motor has just been rebuilt by a mechanic. The tacho didn't work & a 15amp fuse was blowing when I first took it out. The mechanic replaced the rectifier & tacho. The new (second hand) Tacho only works at high revs. I'm receiving 1 volt peak to peak AC at the Tacho at approx. 40hz. The peak to peak voltage increases as do the HZ when the revs increase. The battery voltage stays constant around 12.4 volts. I have bench tested the tacho, injecting a signal. it work find as long as the input signal is above 7 volts peak to peak (AC). I can vary the frequency from 33hz (this = 1000rpm) to 230hz (8000rpm) and the Tacho works fine. What should be the AC voltage coming out of the Magneto and what voltage should the battery charge at ?

[cartex]

My tach does not work on my 94 XP either. I have been trying to figure out how to troubleshoot it. Is there a way to use my multimeter to verify the tach is bad? If the tach checks out, is it the rectifier?? Thanks.