some Duster gauges not working?

Dana67Dart said

Alt guages is not tied to the ivr in any way. BUT, if you had certain electrical issue I could see the alt guage not working causing the other guages to not work but I would expect the engine would not start either.
Sounds like it is time for an electrical diagram, and a lot of trouble shooting.

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You are correct that the amp gauge is not related to the thermal gauges but...
The amp gauge in a 1976 model has a remote shunt. The small wires to this gauge are in the circuit board harness connector. So this model can have a good shunt and a bad gauge.
Sometimes with a engine R&R the chassis ground from firewall to engine doesn't reconnected. This can cause a variety of problems in different models.