RPM Gauge Jumping

[garage91]

Hello All. I am happy to be here and look forward to learning as much as I can. My first problem is this: My RPM gauge likes to jump around whenever it wants. Sometimes it will work and show the correct rpm's, then it will jump to 4000 or so and sit there. Then it will drop back down and tell the correct rpm's again, and so on and so on. The engine is fine and does not fluctuate, just the needle. Where do I start first to fix this problem? And what do I need to do? Any help is greatly appreciated.
Sincerely,
James

 

[85_SS_302_Coupe]

Well there are a couple possible problems. One, your tach could just be going bad and you need a new one, the cable could be bad, or i had a problem just like this once and found out that my battery cable was loose. It had enough connection to start the car but vibrated around when i drove so it lost power to the tach...