Bad Regulator/Rectifier Combo?

I have a 1989 OMC SeaDrive 115.The motor runs fine but my tach is messed up.The tach works fine up to 3000 rpm and when I gave it more gas the tach starts reading lower until I back down below 3000.Then it works fine again.
I checked continuity on reg/rect-it tested ok
I installed a brand new tach(set at 6 poles)-it worked up to 2000rpm and then would drop back to zero when given more gas and then would work alright again when I decreased the throttle below 2000.I returned the tach.
I then installed a 1/2 watt,2200 ohm resistor between the sender/ground terminals on the tach-it worked fine up to 3600rpm but would register no more even at wot.I throttle down below 3600 and it worked alright.
From Teleflex's site I performed 2 tests:1)You should have 12-16 volts DC at IGN and Ground terminals on the tach.I had 12 1/2 volts at fast idle-ok
2)On the Sender and Ground terminals you should have 3.5-5 volts AC at idle and 5-7 volts AC at 2000rpm.Mine had a reading of about 20 volts AC at idle up to 1400rpm.Would this high reading cause my tach to malfunction?

Yep. Sounds like a new regulator/ rectifier assembly.The later reading is way out of spec. http://www.bassboatcentral.com/smileys/wink.gif

Thanks I'm installing one this Friday.