After Market Ammeter?

Dump the ammeter.

When you think about it, it's job is to tell you if the alternator is charging or discharging, which it does directly provided the wires are connected to the right terminals. The issue is that it has to take all the flow, and the long wire runs sometimes don't charge the battery well...or distribute power to anything you added under the hood well.

So, in a way it's measuring "flow"...positive is running to the battery, negative away.

Now, let's think of the safer method that doesn't require all the current to flow through it - Voltage.

With voltage we know we have a conventional "12V" system...

-A typical fully charged battery has roughly 12.5V without the engine or any loads on
-Anything below 12V should be considered discharging
-A correctly functioning alternator should read at very minimum 12.8V to be working, and less than 15V under most circumstances.

So, basically voltage is about the same as pressure...which is resistance to flow.

No reason to take a chance with an ammeter.