fuel gauge problems

Sorry to thread jump, no highjacking intended. But I have the exact same issue, my gauge has been working but sort of intermittenly but the other day I put $20 in and I had more fuel than its had since I owned it and was glad to see the gauge go just past half tank, the next morning nothing and it hasnt moved since, I can see one big purple wire coming from the tank in the trunk, is the ground supposed to come from there as well? Its my understanding sometimes in these old cars the gauge in the tank itself can get gummed up and stuck? I'll tinker with wires and see what happens but any ideas are helpful.