Fred, the voltmeter, temperature, and oil pressure gauges are interchangeable in the clusters throughout the years. The face colors may vary, but these gauges will all operate. The tachometer, speedometer, and fuel gauges are Renix or HO specific.
You can easily check the voltmeter by removing it and applying battery voltage across the + and - gauge terminals. It the gauge deflects properly, then you have a wiring problem to trace out.