How to read an amp gauge

Mattax said

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At fast idle, immediately after start the ammeter might show as much as 20 - 30 amps charging. It would only show that much if the battery is a little lower than normal.
In less than a minute, the current should drop toward zero as the battery charges.

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Actually this depends on several things..........

How large is the alternator (output)
How discharged the battery is, IE it may have been sitting for a couple/ few weeks
Whether you had to crank the "eck" out of it to start, and so on

I used to have an SW 100A ammeter in my beat up Landcruiser, SB Mopar, and the big frame 120A alternator. That thing would BURY the ammeter for a few seconds on a cold start up, and PEG it after using the "wench."

But you are right about one thing.......After starting, it should show some charge, and if headlights, heater, etc are on, you should have "enough alternator" to keep the needle to right of center above idle, and "eventually" the needle should drop down and run at center