High Voltage-Erratic Tach

[fixmyevinrude]

1988 Evinrude 150 XP
Engine runs fine. Voltage gauge reads over 16 volts at WOT and tach is erratic. Sometimes tach only works during cranking and goes to 0 RPMs after start up. Other times tach reads fine at idle RPMs but reads over 7000 RPMs during acceleration and stays there until reduced to idle speed. Lights work with engine off or engine idling but as soon as you accerate the lighting circuit fuse blows. Possible bad rectifier/regulator?

 

[emdsapmgr]

That engine has a combination regulator/rectifier. Usually voltages will get up to the 13.5 volt range, and no more. With the erratic tach, I also would be looking critically at the rectifier/regulator. The tach draws it's pulse counts from the charging side of the engine stator. If it acts up, it's likely the rect/regulator. On another note, just for grins, make sure your two battery leads are really snug on both the engine end and the battery end. If any leads are loose or not clean, battery charging can act up.