I just picked up a 84 Z28 and my gauges on my dash are of.The speedo is way off.For instance i will be on the highway and it says im going like 35.Then my rpm gauge says im hittin like 7500 rpms wich i know im not but still.And the fuel gauge gose way past the full mark ad it also moves around some.So just wanted know ifsomeone could kinda help me out.NOTE the guy that i got the car from was a hack.

 

Sounds like a lot of bad grounds.
Fuel gauge problem, have the same prob, is most likely a bad ground at or near the sender. Full tank is supposed to be like 90 ohms of resistance. 0-90 sounds about right...I know mine always has 118 ohms, could also be a bad float in the tank.

Stock gauges I presume, Speedo is cable controlled, check the tranny and check for proper gear ratio, Posible rear axle change, or binding cable. Tach is electronically controlled to. Posible bad ground at coil.

Lot to check