Edited: another fuel/temp gauge thread, but turns out the harness is melted together

Sorry, I wasn’t clear, I was talking about the solid state instrument voltage regulator.
But your car's IVR is working. Your quick checks show the temperature and fuel gages seem to work. The resistance from the temp and fuel senders appears to off. Find a temperature sender that is closer to 75 Ohms at room temperature or below. Dana covered the aftermarket fuel sender issues Fuel gauge empty when half full, temp gauge low when engine hot, where do I start?

You can also buy some resistors or a potentiometer fairly cheap and make your own tester.