Fuel Gauge and Temperature Gauge Dead

The gas gauge and engine temperature gauge were both working good in my 67 Dart. Both gauges have suddenly stopped functioning. The battery gauge still functions. I did some forum searches and the problem might be the instrument cluster voltage regulator? If this went bad, why is the battery charge gauge still working? Wouldn't all gauges stop functioning if the regulator went bad? Any ideas how to diagnose problem, or should I just go ahead and try replacing the instrument cluster voltage regulator? I found that Auto Zone has one for $37.99.