Broke 20 amp fuse (under cowl), now intermittent tach operation

[lbhsbz]

83 merc 200hp, last trip, pulled up to the beach, shut it down, went to restart and had nothing...found that during the last run, at some point, the glass fuse broke (didn't blow)..and I ran it probably somewhere around 5 minutes with this condition. After replacing (used a blade style fuseholder), I have very intermittent tach operation...occasionally it'll bounce, but mostly sits at zero. I have good power and ground at tach, and on the D.C. Scale saw something on the signal wire with my VOM, so I swapped the tach with a spare I had, no change. I also noticed a high RPM miss on the last pass yesterday...only did it once, not sure if things are related or not.

thoughts? I've looked over the diagram, but can't really understand how losingvthat fuse could cook something. Gotta be either the stator or the rectifier, but it looks like the rectifier, but the rectifier seems just a convenient junction to tie into the yellow stator output. Could I prove the stator bad by switching the tach over to the other yellow output? I have a spare stair, but forgot my flywheel nut socket....so that would mean a trip into town.

[FORBESAUTO]

Yes, you can swap the grey tach wire to the other yellow stator wire. If tach works you go a stator problem.

[lbhsbz]

Thanks. I did the diode test on the rectifier and it passed. Found my flywheel nut socket. Gonna swap the tach wire to the other yellow now and see what happens. Thanks

[lbhsbz]

Didn't bother switching tach pickup...just changed stator. Old stator has zero continuity been red/blue on either side. How'd it run at all? Dunno if it's fixed yet...battery was too dead to fire it, so its on the charger.

[lbhsbz]

Tach worked as soon as I fired it up, then dropped out for about 5 miles, now it's working again. Dunno...we'll see today goes. I'm disturbed that a fuse blowing could take out a 2 year old merc stator.

[lbhsbz]

Back from the dead. Ended up taking last summer off, now have this engine on new boat and the tach still ain't working. Going by what I posted above 2 years ago, I changed switchboxes and the stator, with no change.

I fired it up on the hose the other day and the tach is dead at idle...reads zero. Raise the RPM just a bit and it jumps to over 2000 and bounces around then settles back at zero when I return to idle.

All that's left I think is the rectifier, I think I have a spare

[flabum1017]

check the voltage of the tach sender wire at the tach.... should be around 6 volts or so running. If more, then bad rectifier, if nothing, bad stator or bad wiring somewhere, if it's good, bad tach. Is it charging?

[lbhsbz]

Problem solved. tested the rectifier...had at least one bad diode. Grabbed a spare, also bad....found 4 more used spares...all bad but one. Installed the good one...still don't work. Crawled under the dash (new boat, problem existed with old tach in old boat too)...found no nut on the positive tach terminal. Installed nut, still doesn't work. Power and ground good at tach. Moved a bunch of **** outta the way and found the ground wire connector spun around and touching the signal wire. Fixed that and everything seems good. Battery is charging, stator tested good...so we'll run it.

[flabum1017]

That grounded signal wire probably fried the rectifiers....

[lbhsbz]

That grounded signal wire probably fried the rectifiers....

That would explain one bad one...not the other ones that have never been anywhere near this boat before. Dunno. All good now...and ordered a new spare.