Ammeter intermittently pegs to charge

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midlifecuda

midlifecuda

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Couldn't find a thread dealing exactly with this issue. The ammeter gauge (Stewart Warner) intermittently pegs out on the charge side while at cruising speed (2000rpm). As the rpm's decrease, the needle moves back towards center than climb back to to fully charging as the rpms increase. Then as abruptly as it pegged out, it returns to center where it is most of the time. It may stay pegged for 5 or 10 miles but always returns to center. I do notice the lights get slightly brighter but I have not blown anything. When I first start the car the needle will go slightly to charge and after a few minutes return to center which I suspect is normal. Running a crate 360 (300hp), Mopar orange box, MSD coil and a new battery.
 
We need to start with "what kind of charging system?"

Is this 69/ earlier Mopar or 70/ later Mopar with the "flat" electronic regulator?

If the former, it likely is a bad regulator OR THE VR IS NOT GROUNDED properly

If 70/ later, could be the above as well, or could be a problem with field terminal insulators in the alternator, allowing the "green" wire connection to become grounded intermittently.

If this is an emergency to get home, etc, just pull the green field wire off the alternator and drive home, no alternator working
 
If i had to guess, id guess that you still have an old points style voltage regulator..... and the points are sticking.
Id pull the cover off, (battery unhooked, please!!) and sand the points some, with some fine sandpaper, folded in half.
 
I had this happen with the points type regulator. I changed it out for a solid state unit and it solved the problem.
 
Thanks for the responses. I have the 70 and up VR and the 2 field alternator. I will see if I have a spare VR and start from there.
 
midlifecuda said:
Thanks for the responses. I have the 70 and up VR and the 2 field alternator. I will see if I have a spare VR and start from there.
Click to expand...
Look for a loose connection.
Assuming the SW gage is wired in the same way as the factory ammeter...
Pegging toward charge indicates one or more of the following:
Battery very low on charge or internal damage (such as loose plate)
Uncontrolled alternator output voltage.
Short between the ammeter's battery connection and battery positive (least likely but if you see chafed wires...)

Lights getting brighter with increased rpm suggests voltage is following rpm. However it could do this within a limited range due to high current demands (such as low battery).

Using a hand held voltmeter in conjunction with the wired in ammeter can be a very effective way to narrow down the issue.

In the meantime, give the battery a charge using a charger.
 
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