My vehicle came with an analog Ammeter. When my alternator failed in early '06, I did not know it until the wipers moved at half speed. A voltmeter would have made the failure obvious. The OEM analog Ammeter moving 1/32" to the left went completely unnoticed, perhaps for 150+ miles of highway driving.
An Aftermarket tachometer now resides were the OEM ammeter once did.
I've been planning on upgrading the 11' parallel alternator charge path as it is a doubled 6awg jumper cables crimped before i had the proper tools for doing so. I could then just unhook the original/OEM ring terminal from alt(+) and run hall effect sensor by battery switch, and see total alternator amperage as desired.