Strange tach/RPM problem

[Eddo Rogue]

Not sure if I'm in the right section but here goes...
My tach suddenly started doing weird things. its reading about 1k rpms too high. I will be lugging it in a higher and it will read 3500 rpms. When actually driving at about 3500 rpms, it will read 5k. Electrical diagnosis is not my cup of tea, where should I start?

93 4wd 5spd 4.0 OHV

 

[SenorNoob]

IDK if 93 is the same , but '88 has multiple grounds to be used depending on the number of cylinders. Maybe one came loose?

 

[RonD]

I would look for a 1993/94 cluster with tach as replacement

But yes A9 on the back of cluster is a Ground wire for the tach when using a V6 engine, no ground wire if a 4cyl vehicle, so cluster can do either 4cyl or V6 its the vehicle wiring on that connector that changes

Diagram below
1993 and 1994 are the only interchange matches for those 2 years

If there are no codes(computer uses tach signal as well), then problem is most likely the tach not the signal

 

[Eddo Rogue]

No CEL. I will check that ground wire. Thanks Ron

 

[Eddo Rogue]

Update: The tach randomly fixed itself one day, but then went weird again. I checked some grounds, seemed fine. My battery terminals do have some corrosion. Gonna clean the battery terminals and maybe put in some fresh new cables. Seems when I give the ranger some love, the tach works.