more of a pulse voltage averaging 5 v , do the other gauges oil & temp work if so the reg is fine so it could be the gauge is bad
Chryco is right it won't be a constant 5v. Your other gauges (oil and temp) could be off or reading low too and you just don't know it. A bad VR will put more resistance in the circuit and make it read low. If that's the case only replace the VR with an RT engineering solid state unit which can be found online. If it's not the VR regulator do the following:
-First test, take the fuel gauge wire and bypass the sending unit by putting it straight to ground or the - battery terminal. Don't hold it very long and make sure the ignition key is turned on. Your gauge should peg all the way full. If not, bad news, your fuel gauge is bad.
-Next remove the sending unit from the tank (please try to run the tank empty of gas first and be careful with possible ignition sources). Take one wire from ground and clamp it to the body of the sender while its removed. Next, take the sending wire with your ammeter in series and look at the gauge (remember ignition on) and resistance to the normal sender unit terminal with the float in 3 different positions. The ohm readings should be linear, in other words (full gauge resistance - empty gauge resistance)/2 = half gauge resistance. Report back and I'll tell you what you need to do.
Float empty
Ohms: _____
Gauge reading:_____
Float 1/2 way
Ohms:_____
Gauge reading:_____
Float full:
Ohms:_____
Gauge reading:_____
