Disconnect the wires at the back of the ammeter, being sure to label which wires go to which post. (Take a picture if possible) The meter needle should go to center. If not, you have troubles inside the meter. Repair or replace it. If it does center, reconnect the wire from the starter connection battery cable. Again, the meter should stay centered. If it's wired right, that should be the only wire attached to that post of the ammeter. Reconnect the other wires one at a time. If one is shorted, or has a high-resistance voltage leak, the meter will deflect when the leaky wire is connected.

I'm going to guess you have an internal problem in the ammeter.
Jerry

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