1970 98. The fuel gauge sort of hovers between a little more than 1/4 and and less than a half regardless of what is in the tank. It stays there when the ignition is off. I disconnected the ground at the tank with the ignition on and the needle was the same. With the ignition on I disconnected the wire coming from the tank in the trunk and grounded it and the needle was the same. Is it safe to assume the gauge and not the sending unit is bad? If so, do I have any hope of finding a new one? If not, is there a recommended "gauge guy"? Thanks

 

You grounded the wrong side. You need to ground the side coming from the gauge. The moment you disconnected these two wires, the gauge is seeing infinite resistance, and, with the ignition on, it should move to F or more likely way past it. When you ground the wire coming from the gauge, it should immediately go to E. If the gauge does these two things, it is fine. If not, then as you suspect, there is a problem with the gauge itself.

The moment, though, that you did this, the gauge was also seeing infinite resistance and should have moved to F right then. You wouldn't have needed to disconnect the wire in the trunk. The fact that this didn't happen suggests a gauge problem.

The first thing I would check is the connector on the rear of the gauge cluster. There is a multi-wire connector that has all the wires for the fuel gauge, warning lights, and dash illumination lights, and it can get jiggled loose.

 

I have a similar problem. So far, I found somebody that rebuilds guages: John Wolfe and Company in Ohio, http://www.antiqueinstrument.com/ will rebuild the sending unit or the guage. I need to go back and run the diagnostic again, AND find the correct part number for more searching. The wiggly wire sounds a lot cheaper than a new sending unit.