[strictlypersonl]

Let me clear up a few things...

The ammeter only indicates the net current in and out of the battery. You can have a 100A load and a 100A alternator and have zero current through the ammeter.

Once the car starts, the ammeter will likely have a strong - and temporary - period when it's recharging the battery, after which it will settle down to near zero. (That's only the current going through the ammeter, not the current flow from the alternator into all the loads.)

It's not the end of the world to show a negative flow, as long as it's temporary. In fact it's normal. We've only become used to never seeing the reverse current because newer cars don't have a gauge.

That said, a voltmeter is really a better indicator of the state of the charging system than an ammeter, but it's not a necessity for a high-output alternator. For certain applications, I can create a shunt that bypasses about half the current around the ammeter.

If you want to substitute a voltmeter, I have more electrically-efficient ways to do it than as described above, at least for the later harnesses that use the big plugs between the main and dash harness.