74 duster gas guage

first of all thank you all for the chance to be on your forum and all the work you guys do!! ! you were all a big help figuring out my codes on my new to me 74 duster. I have one more problem. gas gauge doesn't work. I connected a ground wire to the connector that connects to the sending unit. turned the key on gas gauge goes up to full. if I remember right this means sending unit is bad? there is a connector on the metal line b4 and after the hose so I would guess tank is grounded. any and all help appreciated. thank you