Low Charging - Alternator Problems?

[fastsvo]

Hi Guys,

I have a 165amp 3G alternator (large case) on my '91 that was purchased from a reputable seller on ebay aka "zbeav@aol.com" a few years ago and not many miles have been driven on the car (it's been in storage mostly).

Ok, this alternator has always done an excellent job of charging the system and the other night I noticed the alternator gauge was staying down below the 1/4 mark and would not budge as the rpm's rose.

Put the charger on the battery and was surprised to find that it did required some charging time (car ran pretty good before hand).

So here are tests that I have performed so far:

Engine not running & ignition on

1) Disconnected the D connector with the 3 wires and measured the voltage on the lt green/red wire = 12 volts CHECK

2) Reconnected the D plug to the alternator and probed the greed/red wire. I should be seeing 2.4 - 2.6 volts here but I got 3.8 volts ..... a problem? I understand if I had no voltage at all here, then I would have had a failed regulator.

Engine Running & ignition on.

1) Probed the green/red wire and I should be seeing battery voltage minus .25 to 1.0 volt. My battery at this time was @ 12.92 volts (discharging?) and probing this area got me 12.15 volts.

2) Probed red lead to the charge stud on back of the alternator. The battery at this time was showing 12.5 volts. The Charge stud varied on my DVM between 18.10 - 19.15 and sometimes just 1_.__ (did it exceed the value? DVM set at 20volts DC).

Is my alternator perhaps overcharging the system here? Does the 3.8 volts received from the D plug point to a bad voltage regulator? Bad alternator?

I have yet to pull the 200 amp blade fuse and measure the resistance.

Any help would be appreciated here.

Thanks in advance,

Eric

[cesarthepleaser]

sometimes the voltage regulator gets stuck and keeps voltage flowing even when not using your car. thus draining the battery. also your alternator could sometimes not be getting signal to charge due to a bad fusible link near the battery. i think its the thick yellow cable that goes from (driver side) to passenger side thru core support to alternator. had these issues on two of my foxes and one a buddys fox.

but have the alternator tested at autozone and if its good. look for the fusible link that might be bad.

[ka0tyk]

keep in mind the stator wire runs from the battery main harness, to the ignition switch, then thru the dashboard cluster, thru the battery gauge then to the alternator.

try taking a wire from teh battery to the stator and check the voltage then. if its where it should be, chances are theres a bad connection to/from the cluster or the cluster gauge itself. i had this happen on my old fox and ended up replacing the cluster in the end because i simply couldnt get the alternator to charge.


http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

its all located in teh bottom right corner.