Got an 84z, the tach reads straight down and the oil sender is straight up at all times. Neither move, anyone know how to fix that?

 

Could be a lot of things; my first GUESS is the printed circuit on the back of the cluster. It's old and they tend to layers tend to separate exposing the traces to corrosion and damage. The printed circuit for the back of an 84 would come from the 82-85 years only. Cluster printed circuits from 86 & up are different.

You might be able to "hack" it back together and get it working. You'd have to pull the cluster to investigate...............

EDIT: "GUAGE" Printed Circuits.... (NOT "warning light")
82-85 PrintedCircuit PN= 25045480
86-89 PrintedCircuit PN= 25081605