Sounds like it to me, my 68 indicated the correct quantity of fuel until I turned on the lights, then it pegged past full. I took apart the rear wiring harness in the trunk and re-ground the tail, brake and backup lights, then a new ground for the fuel sending unit and now things work as they should.
Although the float and arm of your fuel sending unit could be physically stuck in the full position resulting in a full reading.
Al.