Years ago, I posted here, because I thought I had some weird amp gauge. Turns out my mechanic was an idiot. Big surprise there.

I was thinking back and all of a sudden wondered why I was trying to replace the amp gauge in the first place. I believe the same mechanic told me that I needed a new gauge because the battery wasn't charging like it should and because the gauge wasn't functioning and it had a built-in voltage regulator, that was causing it to run low. I can't remember offhand any other symptoms that would have made us diagnose the ammeter as the culprit.

Any simple/good way to test whether the ammeter is working correctly? I have the dash apart right now and could easily replace the ammeter with the NOS one I bought, but if there's no need...

When the car is at curb idle, and the headlights are on, I see the needle move back and forth between Charge and Discharge, slowly. When the headlights are off, the needle pretty much stays centered. Haven't noticed any other funkiness.

The ammeter is there to show the current flowing into the battery (charge) and out of the battery (discharge). Start the car and take it for a drive without lights being on. Right after you start, the ammeter should show slight to moderate charge at fast idle and cruising as the alternator refreshes the charge in the battery. That should drop off towards no charge (middle of the ammeter) as you drive around.

Mmmmm... there is no built-in regulator in the ammeter if that was what you're mechanic was saying! Ammeter sensitivity (i.e., how much deflection it shows for a set amount of charge or discharge current) seems to be pretty variable.

If you put a voltmeter on the battery when you are at curb idle with the lights on and when the ammeter is moving back and forth, the voltmeter will very likely show the voltage going up and down in a fashion corresponding to the ammeter fluctuations. It really ought to not have fluctuations, but that is an issue in the regulator or its connections, not the ammeter.

If you want to do a simple test of the ammeter out of the cluster, then I would use a headlight as a load to test it. Remove a headlight connection and jumper the ammeter to the battery on one side and to a headlight prong on the other, and of course ground the headlight prong that is normally grounded through the headlight connector. The ammeter needle ought to move slightly to one side or the other as the headlight element should draw 3-4 amps and should glow brightly. Reverse the connections to the ammeter and look for the same ammeter movement in the opposite direction.

Also, check the ammter terminals closely and carefully for any signs of rust or corrosion or any evidence of having gotten hot. That is a bad sign.