However it might not be just the ground. A couple of years ago I showed with images how 90 ohm sending units are converted to 30 ohm units. Solder is crudely dropped on the winding until the ohm gauge hits approximately 30...after all anyone who didn't sleep through electronics 101 knows you only need to connect those winding wires to reduce resistance. What this does is create dead spots, spots where the gauge is given either the wrong or no electrical input and this mickey-mouse approach can cause the tiny wire in the winding to break. I bought one of these senders from a well-known supplier of parts which a lot of people seem to trust. It was trash from the word go. I won't tell you the supplier's name because he didn't make it, but I will tell you he refused to refund my money and always overcharges for shipping. The best (and I mean the best by a very long shot) sending unit is sold on eBay by a seller whose ID is renbusan. He and I have communicated and he knows his stuff. Here is the unit you want:https://tinyurl.com/y3lhydzg
Here is what the Chinese-modified sender looked like when I finally got so tired I removed it and took it apart:
The second image shows what the unit renbusan sells is like...nylon, neat & clean with the windings set into nylon and not running in a U shaped arc but running in a C shape with a wiper arm. Much better design. Good luck!