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Discussion Starter #1
Guys,
Having an issue as of late, my 3G alternator is not charging, my last 3G alternator bearings went out, ordered a new 3g alternator, installed, checked voltage it was OK then a week later battery is dead, return and replace alternator again and now only getting 12.2-12.5 volts from back of alternator and battery. I have followed this check list posted below and am stuck at the second section checking voltages at the D connector

I have 12 volts on the yellow wire but 0 volts on the Green/red stripe (checklist says it should be 2.4 volts with KOEO.

Also my 86 does not have an alternator or charge warning light on the dash, so trying to figure out how to fix the (exciter wire for regulator) 0 volts on the GREEN/Red stripe wire in the D connector. Not sure how much of this checklist is pertinent to an 86 but it did say it was for 3G.

Any help is appreciated. Thanks!

Here is the checklist

Do all of these tests in sequence. Do not skip around. The results of each test depend on the results of the previous
tests for correct interpretation.

Alternator troubleshooting for 86-95 5.0 Mustangs:
Engine off, ignition off, battery fully charged.
1.) Look for 12 volts at the alternator output. No 12 volts and the dark green fuse link between the orange/black
wires and the battery side of the starter solenoid has open circuited.
3G alternator: Look for 12 volts at the stud on the back of the alternator where the 4 gauge power feed wire is bolted.
No voltage and the fuse for the 4 gauge power feed wire is open or there are some loose connections.
2.) Look for 12 volts on the yellow/white wire that is the power feed to the regulator. No 12 volts, and the fuse link
for the yellow/white wire has open circuited.

Engine off, ignition on, battery fully charged.
1.) Alternator warning light should glow. No glow, bulb has burned out or there is a break in the wiring between the
regulator plug and the dash. The warning light supplies an exciter voltage that tells the regulator to
turn on. There is a 500
ohm resistor in parallel with the warning light so that if the bulb burns out, the regulator still gets
the exciter voltage.
Disconnect the D connector with the 3 wires (yellow/white, white/black and green/red) from the voltage regulator.
Measure the voltage on the lt green/red wire. It should be 12 volts. No 12 volts and the wire is broken, or the 500 ohm
resistor and dash indicator lamp are bad. If the 12 volts is missing, replace the warning lamp. If after replacing the warning lamp,
the test fails again, the wiring between the warning lamp and the alternator is faulty. The warning lamp circuit is part of
the instrument panel and contains some connectors that may cause problems.

2.) Reconnect the D plug to the alternator
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see
2.4-2.6 volts. No voltage and the previous tests passed, you have a failed regulator. This is an actual measurement taken
from a car with a working electrical system.

Engine on, Ignition on, battery fully charged:
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see
battery voltage minus .25 to 1.0 volt. If the battery voltage measured across the battery is 15.25 volts, you should see 14.50 volts
 

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Discussion Starter #2
I have found a work around for the time being, tapped into red wire of IAC circuit to Green/red wire on pigtail. alternator is now charging. Still confused as to the 86 specific wiring and no charge warning lights, that was throwing me off looking at my dash cluster and ignition switch wiring.
 

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IAC is pule width modulated control

probably not a good idea
 
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