The "middle mark" of the gauge (half way between "D" and "C") is "normal" if everything including the engine is turned OFF. The middle mark signifies there is no current flow, or that battery load is balanced by battery charging. With the engine running, the ammeter should deflect toward "C". The amount it deflects is dependent on the current output of the alternator, balanced against the electrical load at the time. With the engine OFF and any electrical device turned ON, the ammeter should deflect toward "D". The amount of deflection will depend on the amount of the current draw from the battery.
From decades old memory
- if the ammeter needle "never moves," then
remove and check the two short 4-amp fuses located in the fuse box (or in the engine compartment wiring harness in two separately located in-line fuse holders). Both fuses must be removed to be checked, because each fuse is connected to power and are in series with each other through the ammeter. When both fuses are removed, make sure there is power available to both fuse locations in the fuse box (or the in-line fuse holders).
If both fuses are receiving power, the fuses test good, and there is no corrosion on the fuse box clips (or fuse holder clips), then there is an "open" either in the ammeter or its wiring. Re-install
either one of the two fuses and check for power at
both fuse box clips (or in-line fuse holder clips) for the fuse that is still uninstalled. Power at only one of the fuse clips indicates an open in the ammeter or dash wiring (e.g., tarnished connections at the PC Board, bad gauge, bulkhead plug, broken wire, etc). If you have power at both fuse clips, then there may be a gauge calibration issue.
Recalibrating the ammeter is possible, but first you need to check the above and report what you discover. Hopefully, a bad fuse or connection will be the issue.
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