Need help testing a 1975 valiant Instrument cluster

It's easy to test whether the gauges are completely bad. Not so easy to see if they're accurate. A simple Ohmmeter will tell you if the gauge circuit is still good. The location of where the needles rest will give you some indication if the gauges are cooked. You want the needles to rest just below the E mark. If they're way below that mark, they've probably been overheated.