The amp / alt gauge has nothing to do with the rest. If the headlights work, and if turning them on with everything else off does not show a bit of movement to the left, then someone has bypassed the gauge, or it is "stuck." It is fed by the large black and large red wires.........BE CAREFUL!!! Full battery current UNFUSED is present on those leads.
I've posted hundreds of things on gauges. Standby.........
67dart273, gauge tester - Google Search
Below someone posted the resistance test values for one of the service gauge testers. With this you can use an ohmeter...........
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HERE IS HOW the gauges OTHER than ammeter work:
The cluster is supplied switched power from the ignition switch...........which powers the gauge regulator various called IVR, instrument limiter, etc.............and the output is branched off to fuel, temp, and oil if you have it
ALL THREE GAUGES are identical electrically. That is, a certain resistance at the sender will result in the gauge needle reading the same on any of the gauges
From the gauges, the sender wires lead separately to the oil, temp, and fuel senders TO GROUND
Some things..........
Some problem areas...........
ALWAYS a suspect is broken/ loose/ corrode pins in the cluster/ PC board connector, either a the connector or at the board............
