I just replaced my fuel tank and the sending unit. I tested the sending unit and it is registering 0 - 90 ohms like it should. The fuel gauge will only show 0 to 1/4 no matter how "full" the sending unit float goes.

I checked the lead wire going "to" the fuel sending unit and has 6 volts. Is this right? The ground is good and clean. Should I assume at this point the gauge is bad?

The car is a 73 LT.

Ground the wire going to the tank unit...the dash gauge should go to full. This will not harm the gauge. If it don't read full the dash gauge is bad.

I grounded the brown wire in the trunk that goes goes to the center of the sending unit and the gauge needle went to E. How can I tell what voltage I should be seeing out of this wire? I'm showing only 6 volts.

Grounding your fuel sender wire should read 'E' or empty on the guage. Without any connection, it will usually go way past full. If you connect the wire back to the sender and the guage goes 0-1/4, then I'd suspect a shorted wire around the tank. Maybe the wire is touching ground on top of the tank?

I've got the same problem on my '74 Z. I've been a little too busy to sit down and figure it out. Those ideas will give me a place to start to find the problem.