I have replaced both the Alt & external regulator (twice) on my '72. The amp meter (millivolt meter) still reads about a needles width or less on the discharge side of the guage at idle & goes even deeper when the radio or lights are turned on. What gives?

I'm no expert on this - but I'd check all your wires and connections for corrosion and a high ohmmeter reading, indicating it's bad. My guess is the charge isn't reaching your battery.

Of course, that assumes your BATTERY is still good, which is easy enough to test at any auto place.

I'm no expert on this - but I'd check all your wires and connections for corrosion and a high ohmmeter reading, indicating it's bad. My guess is the charge isn't reaching your battery.

Of course, that assumes your BATTERY is still good, which is easy enough to test at any auto place.
the battery is fine. It's an optima redtop about 4 mo. old & is always on a battery tender.

Take it to your nearest auto parts store and have them check the system on the car. Factory guages can go bad. They can test your starting, and charging system and bat. on the car. And will be able to tell you if there are any voltage drops too high for the system.

if it only shows a discharge at idle but comes up when you speed up the rpms perhaps this is normal....does your battery stay charged up when you are driving? Alternators need to spin fast to make them charge.....just a thought

if it only shows a discharge at idle but comes up when you speed up the rpms perhaps this is normal....does your battery stay charged up when you are driving? Alternators need to spin fast to make them charge.....just a thought

Thing is that it really barely gets past the "0" I guess I'll have to put a meter on it.

The ammeter reads current to and from the battery. If the battery is fully charged the needle will not go much in the positive direction. If the alternator isn't producing enough power at idle, the ammeter will go in the negative direction.

The ammeter reads current to and from the battery. If the battery is fully charged the needle will not go much in the positive direction. If the alternator isn't producing enough power at idle, the ammeter will go in the negative direction.
I never really understood the usefullness of an Ammeter in older cars. :clonk:
Seems to me a simple voltmeter, as what is installed nowdays, would be much more informative.

I never really understood the usefullness of an Ammeter in older cars. :clonk:
Seems to me a simple voltmeter, as what is installed nowdays, would be much more informative.

In 72 the amp guage is really a millivolt guage

The usefullness of an ammeter is as follows ; You can push voltage and at the same time not have current flow. With our alternators you'll rarely ever see current flow changes without a concurrent voltage increase.

On my car I want to know that I am seeing current flow. I am satisfied that I have voltage everytime I start my car. The ammeter gives me more information about what is actually happening inside my alternator than a volt meter does.

Recently someone mentioned that there was a danger element with ammeters because of the heavy guage wiring needed and the potential for shorts grounds etc. My wiring skills rise above that. When I put an ammeter in my car its wired such that those concerns aren not there.

Older Ammeters were actually shunt styles. They had an inline resistor that found the voltage difference on either side of the resistor and translated that into Current. In these type of ammeters large wires and large currents were not needed to give the information. But a true ammeter does need to have all power from the alternator to come into the car, through the meter, and then to the battery to be accurate.

In 72 the amp guage is really a millivolt guage

Every gauge is an ammeter, a D'Arsonval meter movement is current operated.

Recently someone mentioned that there was a danger element with ammeters because of the heavy guage wiring needed and the potential for shorts grounds etc. My wiring skills rise above that. When I put an ammeter in my car its wired such that those concerns aren not there.

That maybe true but my conserns are with the 40+ year old factory wired gauges in many of our cars. :(

That maybe true but my conserns are with the 40+ year old factory wired gauges in many of our cars. :(

Bill your sig line says you have a 70 and a 72. In both cases the ammeter really is a zero centered millivolt meter not the older style shunt ammeter with higher current flow.

Either can be informative but neither by itself can always tell you what is wrong when there is a problem. On the otherhand either can indicate there is no problem when there really is.

1. A voltmeter can read correct voltage all the time but not tell you it's constantly trying to charge a bad battery, one that is not holding the charge. If the voltage is always low is it the bat or the alt/voltage reg?

2. A ammeter can indicate no charge or discharge even though your alt is only putting out 11v and that's what the current bat charge is. It's enough to fire the ignition and keep the engine running but not enough to start the car again if you shut it off. If it always shows charging is it a bad battery not holding a charge or is the regulator shot and trying to charge the battery to 18v?

Like I said neither is perfect but both are useful in most cases.

I have replaced both the Alt & external regulator (twice) on my '72. The amp meter (millivolt meter) still reads about a needles width or less on the discharge side of the gauge at idle & goes even deeper when the radio or lights are turned on. What gives?
All this means is that your alternator is not working at idle. What amp alternator did you use? Assuming that car we are talking about is the one in your sig, this may or maynot be a problem. What is your idle speed?

if it only shows a discharge at idle but comes up when you speed up the rpms perhaps this is normal....does your battery stay charged up when you are driving? Alternators need to spin fast to make them charge.....just a thought
Correct. This was a problem, especially on the factory Hi perf cars that had the larger deep groove alternator pulley.
Thing is that it really barely gets past the "0" I guess I'll have to put a meter on it.
It is not supposed to if the battery is fully charged.