Tachometer Quit working JD 4400 tractor

[ohiogar]

Am in the process of restoring a 1998 JD 4400 Tractor with around 50 total hours on it from new. I have about 3 hours run time on it myself.
The tachometer worked fine and just quit all of a sudden. The hour meter works fine.
ALL of the factory safety's are functional. This is a pre computer machine.
I believe that the tach works off of a pulse from the alternator. A Trusted auto electric motor friend
tested and said the alternator is just fine. I even tried with a second used alternator.
I have traced all of the wiring and it also seems fine.
ALL of the relays have been switched around with extra's and have no effect on system.
I am clueless here. Any Ideas appreciated.
Regards from Ohio
gary

 

[Roadworthy]

Is there any way to test the tachometer itself, that is a substitute input to see if it reads?

 

[ohiogar]

I really do not know
I have read that the hour meter works off of the power supplied to the tachometer

 

[Roadworthy]

If there is no mechanical cable driving the tach it probably does feed off the alternator - counts pulses or something - not sure. Are your hour meter and tachometer both in the same unit or are they two separate instruments? That can work both ways. Unless it's a broken wire somewhere, unless you are familiar with working on instrumentation you should send the unit out for repair.

 

[ptsg]

Try wiggle the plug at the back of the dash. Or pull it out and check for corrosion on the pins. Sometimes it's all it takes.

 

[ohiogar]

Thanks I have done that many times. I have been over under inside and out and it will not work. BUT the hour meter works which is confusing
It is a new aftermarket dash cluster. Under advisement it just felt right to put
a new unit on a tractor with so many obvious signs of low hours.

 

[Agvg]

Is there any way to test the tachometer itself, that is a substitute input to see if it reads?

A signal generator could be used to make the pulses.

 

[ohiogar]

I have no knowledge of a signal generator. will research it.
I believe there is a pole on the alterntor that supplies that pulse.
How would one test that?
Thank You

 

[Williy]

You can get a meter from amaxon.com
You don't need the high dollar one just
get a cheap one for the price of the high
dollar one's u can get 4 or 5 cheapies!

willy

 

[rScotty]

It seems too simple, but doesn't the shop manual have a schematic?
BTW, does the JD4400/Yanmar engine clock measure "key-on" hours or engine RPM converted to hours? There doesn't seem to be any rule on this.