Hey guys im having some trouble with my 89 ford, ive replaced the sending unit along with a new fuel pump in hoping that it would fix my gauge from jumping around and not reading full when the truck is filled up and since i replaced it..it seems that it fixed it where i can tell how much fuel i got but there's a couple things still not working. First it still doesnt read all the way full when i fill up the truck and when i go from a start the gauge still moves whenever the gas slushes back and fourth but im also wondering maybe my whole gauge cluster might need to be changed out cause my temp gauge dont work along with oil pressure gauge, with the oil pressure gauge it goes all the way right where its reading a good oil pressure even though my truck use's a quart or so...so i need you guys advice on how to fix this issue.
Not familiar with the 77 instrument panel or electrical circuitry. If all the gauges are effected, and the 77 instruments operate off the Constant Voltage Regulator (CVR) then it could be faulty. Basically acts as an electrical shock absorber in that it regulates voltage from between 0-10 volts to the instrument panel, taking a volt meter should be able to determine if it's working. In addition, had similar problem and found the instrument cluster was not grounded sufficiently so I add an additional ground strap and ran it from the metal part of the cluster to the brake pedal assembly and it settle the fluctuating readings?? Anyhow, some thing to consider.