Alternator issues?

[enyap798]

My name is matt, i'm from right around Pittsburgh, PA.  i posted a few pix of my rig.  i've been following this group for a few months, but haven't contributed till now.  it's cold around these parts now so i haven't been able to tinker with it, but my alternator isn't charging i don't believe, and my fuel gauges don't work as well as my charge - discharge gauge, just stays in the middle all the time.  got 440-3 should i read anything from the 2 smaller posts on my alternator? are these symptoms of a shot alternator?  comments welcome, and i hope to be able to help out when i can

[Clyde9]

You should have over 12 volts from the large post (which is connected to the positive terminal of the battery, or voltage splitter which goes to the positive terminal of both batteries) to ground when spinning (engine running). If not, yes, it may very well be shot, I would bring the old alternator to NAPA and have them test it before you buy a new one. They will be happy to swap your core out for a new one if it is bad. Great to have you aboard. Again, welcome aboard, and thanks for your contribution too!!
clyde9

[denisondc]

   The ammeter not reading much can also be caused by aging of the ammeter itself, and the tiny pivots for the indicator needle being gummed up.  Hard to fix; but if you ever open up the instrument cluster, try to put a very tiny drop of light oil on those pivots.
   There are 3 terminals on the typical 70's mopar alternator, not including the ground connection - which is just as important as the other 3 terminals.  The big terminal takes the output of the alternator to the electrical system, via an amazingly long run of wires that are as old as your Winny.  Its surprising they still work at all in view of the amount of corrosion that can occur over the years.
   The two small terminals on that alternator supply current to the field coil on the rotor inside the alternator - which provides the spinning magnetic field that lets the alternator create electricity.  If you were to measure the voltage on them - with the engine running and the alternator spinning, you would see about 11 or 12 volts on one of the terminals, (this would be anytime the igntion was on) and a lower and varying voltage on the other terminal.  The lower the voltage on that other terminal, the higher the output of the alternator is supposed to be.  I think the voltage varies a few times a second, and if measured with a digital VOM, the vom would just go nuts!  An analog meter with a needle would show it moving up and down, changing both as the battery got charged up, and as the engine speed was raised or lowered.   If you were to short that terminal to ground, the alternator would go to its maximum output.   That is how the (operating) output of the alternator is measured.
     It is entirely possible for an alternator to lose 1/3rd or 2/3rds of its output.  It is really a 3 phase a.c. generator with 3 banks of diodes to rectify the a.c. into d.c.  If one bank of diodes fails - your alternator can still work using the other 2 banks; at 2/3rd capacity.  Etc.  Though I think its more common for the brushes to wear out or for the ball bearing at the front of the alt. to fail. 
   If your fuel gauge doesnt indicate - that can be a bad sender unit in the fuel tank, or a bad wire from the tank top to the gauge.  It can also be a bad gauge.  The mopar gauges work from a "voltage-limiter" that is in a small metal goody under the dashboard, near the cluster.  It looks like an automotive circuit breaker and works on the same principle.  If the ignition is left on, this little 'limiter' will be hot to the touch when working.  It also supplies voltage to the oil pressure and water temperature gauges.  So if those other gauges are working normally, then its not the voltage limiter that is bad.   As of recently, the mopar sending units were still available from www.jcwhitney.com.  Do a keyword search on 'float'.
  I grew up in Ambridge, back when it was a steel mill town.