Early A body Fuel Gauge Instrument Cluster Question.

If both fuel gauge and temp gauge stopped at the same time, the limiter is the likely culprit. Ohms meter will tell if the gauge is alive or not. 5 volt post to sender post should show approx' 20 ohms. Same for temp gauge.
There is a way to open this type gauge without drilling and replacing rivets/brads. Lets hope you dont need that detailed.