I'm not aware that Mopar alternators, at least the common, older style frame, even used a "ground wire" so I'm wondering if you didn't mess with something different
One problem, is that the traditional old style so called "round back" alternators have become notorious for poor output at low RPM Too bad you didn't ask first, probably you should have at the LEAST gotten a mid -70's "square back" (which have two field connections, known correctly as "isolated field," know INcorrectly as "dual field") and even if using your original style regulator, the 70's style can be used by grounding either one of the field connectors, then hook up as your old one
A PROPERLY operating system, with a good battery, good wiring, good regulator and alternator, will show a charge, the amount depending on how "low" the battery got while cranking, or maybe lowered a little more if warming up at idle in the parking lot with lights and heater on.
So the meter will go up or down with engine speed, until the battery is charged, then it should run pretty much "centered." On these older cars, the ammeter WILL discharge with lights/ heater at low RPM, and so will then charge a bit to "get back up," and after cruising for a bit, should go back to center
NO1 suspects with "wild acting" ammeter probably are:
A bad regulator or alternator, and "new" or "rebuilt" does not mean "it works properly"
On most Mopars, problems in the bulkhead connector. Your car may have the main (large) battery feed and charging line SEPARATE from the bulkhead connector, but the IGNITION RUN wire which FEEDS the regulator most certainly goes through this connector.
The bulkhead connector is probably the no1 problem with wiring in these older, unrestored cars
Please read this MAD electric article, which shows some of the problem
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
You need to get yourself a digital meter, and do some testing, as well as a factory shop manual. You can download some of them for free right here:
(The '66 manual would be close enough for most stuff in your car but I'm not sure when the bulkhead connection changed from "separate" to "through the connector" for the charging line
http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=manual,+download
and more yet over at "MyMopar"
http://www.mymopar.com/index.php?pid=31
Some things to suspect, not in order:
A just plain crap regulator, or a poor ground between the regulator and battery neg.
A poorly rebuilt alternator
A break or bad connection in the main charging wire from the alternator, through the bulkhead, through the ammeter circuit, back out the bulkhead, and to the battery
(refer to the simplified diagram in the MAD article)
A similar bad connection in the regulator circuit
Some tests to start with:
With the car running to simulate "medium cruise" IE a good very fast idle, measure the battery voltage right at the battery. It should in NO case be below 13.5, or above 15. 13.8--14.2, when WARM is normal
Test for ground at the regulator. Again with engine running, stab one probe of your meter on the battery NEG post, and the other probe directly onto the regulator mounting flange. Stab through any paint, chrome, rust. You WANT to see a very low reading, the lower the better. OVER .2V (two TENTHS of a volt) shows that there is not a good ground between battery, block, body, and regulator
Now put one probe on battery POS, the other probe on the insulated output stud on the alternator. Turn on headlights, heater, and make sure it's charging "some" IF the voltage is much more than 1/2 volt, you have a problem in this charging line
Next shut off the engine, and turn the key to "run" engine off
Put one probe on the battery POS post, the other probe on the regulator "IGN" terminal. You want to see VERY low voltage, anything over .2-.3 (3 tenths of a volt) means you have "voltage drop" in the ignition harness
Your path for this is battery -- fuse link -- through the bulkhead -- ammeter circuit -- ignition switch connector -- through the switch -- back out the switch connector (dark blue IGN run wire) BACK through the bulkhead -- to the ballast resistor and regulator
OF COURSE make SURE the belt is in good shape and properly tight.
