Senders are not voltage specific
He stated he has 12 volts and a 12 volt gauge. No resister needed.
If this is a new 12 volt gauge there are 2 common issues to check.
Good grounds, and clearance at the needle. The reproduction 12 volt gauges have a needle that sits higher than original. Sometimes it get pinched by the bezel. So check for clearance.
Another common error is the ground. There is a metal tab on back of the fuel gauge with a solder glob..this need to contact clean metal in the cluster. If you refurbished the cluster and painted it you'll need to clean the paint off so the back of the gauge touches metal
Let us know what work you have done to this gauge. There is more troubleshooting to do.
