Testing fuel sending unit

The gauge does not register. Just bought the car and the owner replaced the sending unit a couple of years ago and said it was working recently. Before pulling stuff I need some reminders of how to start troubleshooting. It's been a few years since doing this and I'm not remembering all the steps.

Is this enough info?

the sending unit should read from 15-85 ohms depending on how full empty the tank is.

Pull the wire off of the sender and use a Ohm meter to see if it(the sneder) is working, showing a ohm reading or not If no reading at all it is not working

Pulled the wire and got 86 ohms. So I guess that means the sender is at least working. How accurately it is working remains to be seen. So next I am going to check if there continuity along the wire from the terminal to the gauge. If that is OK how do I check the gauge without doing it harm?

Grounded out the terminal back at the tank and the gauge went to full. I am assuming the gauge is good. So, if there is 86 ohms at the sender, the wire is good, the gauge goes to full when grounded and yet the gauge doesn't register with the terminal connected to the sender that is grounded where is the problem?

Do you have the fuel gauge ground strap like in this photo?

http://www.cuda-challenger.com/cc/index.php?topic=70229.0

No but I was grounding it other ways to test it to no avail. I have now gotten the unit out of the tank and it is a bit crusty. It's not original but it is without a float, screen and was stuck in one position. With a good ground I can get it to move the gauge now that it is no longer stuck and it looks accurate. Looks like a replacement unit and new ground strap is in order. It is good to have helpful friends. Thanks to all.

So the float is in the tank somewhere and the screen disintegrated. Can always get a replacement float and screen if it still works good. Reproduction ones are not the best, just ok. You can get those floats and ground strap on ebay and other places.