The fuel gauge on my '65 Impala reads full all the time. It used to only come up to about 2/3 full, but as you drove, it would go down, so I always figured that when it showed empty, I had about 1/3 of a tank left. Now it just stays on full. Do I need a new sending unit, or could it be something in the wiring? Thanks.

Randy

YES!

Randy there should be a connector in the trunk, near the latch if I remember right, and I think it should be a tan wire. If you disconnect the wire and ground the end that goes to the front of the car with the key on the gauge should go to empty. If the gauge goes to empty than that means the wire from there and the gauge are ok and you most likely need a sending unit, but make sure the ground wire that comes off the sending unit is good.

Yes, I need a new sending unit or yes it's the wiring???

It is most likely one or the other. If you isolate the sending unit and determine it is OK, then you must check for a wiring problem. Some suggestions on the wiring is in a post above.