The fuel gauge on my 68 camaro reads just past a quarter tank no matter how much gas is in the tank. I unplugged the sending unit from the harness in the trunk and the gauge went to full. I then grounded the harness end and the tank went to empty. Does this mean something's wrong with the sending unit? Are there other things that can be checked out before dropping the tank? Thanks

The sending unit is probably the issue. I would bet you need to drop the tank for this one. It is a variable resistor and in this case it is not varying.

-Mark.