Electrical Alternator not charging

SHOme

Active Member
Nov 16, 2018
63
40
28
51
Maryland
I need help again. I went through the procedure below. I had no battery warning light so I replaced it although it was good. With key on and engine off. I have 12 volts on the green/red wire going to the regulator but the battery warning light will not illuminate. If I have 12 volts on the green/red wire at the alternator how can the dash light not be lit? Isn't this wire coming from the light? My battery is fully charged and my alternator tested good.

This car is going to make me a pro troubleshooter.

Red color text applies to cars with a 3G alternator.

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.

Simple first step: Remove the alternator and take it to your local auto parts store. They can bench test it for free.


Use a safety pin to pierce and probe the insulated connectors from the rear when doing tests with the connector plugged into its' mating connector.

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. Good
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. Good

Engine off, ignition on, battery fully charged:
The instrument cluster must be in place and working properly for the alternator to charge. The indicator light is an essential part of the charging circuit.

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 instrument cluster. 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 voltage regulator. This is an actual measurement taken from a car with a working electrical system. If you see full or almost full12 volts, the regulator has failed.

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 measured across the battery is 15.25 volts, you should see 14.50 volts

Familiarize yourself with the following application note from Fluke: See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .
 
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fredfifty

Well-Known Member
Nov 23, 2011
318
60
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SF Bay Area
try to swap clusters and see if that works. on mines, the rear of the cluster had a bad connection so it wasnt illuminating the battery light at koeo. if that light doesnt come on then the alternator is not charging the battery.
 

SHOme

Active Member
Nov 16, 2018
63
40
28
51
Maryland
Am I supposed to get 12v from both of the Black/orange alternator outputs? I am referring to the two wires on the left side of the plug below.
IMG_20200304_164039.jpg
 

SHOme

Active Member
Nov 16, 2018
63
40
28
51
Maryland
try to swap clusters and see if that works. on mines, the rear of the cluster had a bad connection so it wasnt illuminating the battery light at koeo. if that light doesnt come on then the alternator is not charging the battery.
I wish I had one to swap.
 

SHOme

Active Member
Nov 16, 2018
63
40
28
51
Maryland
I pulled instrument cluster and got light to come on when powered directly from the battery though the circuit on the back. That's eliminated.
 

SHOme

Active Member
Nov 16, 2018
63
40
28
51
Maryland
I have continuity on the green/red all the way to the plug at the instrument cluster. The circuit on the instrument cluster has continuity. There is 12v present at the alternator with the key on. Light will not come on. What does the ignition side of the light do? Just provide the 12v? If so how can the light not come on? Resistor bad?
 

Blown88GT

Founding Member
Nov 13, 1999
2,144
505
164
Palm Beach Gardens, FL
That's a 2G alternator power plug. The black/orange wires run parallel to each other to increase the ampacity.
The connector is the weak point of the design. A bit of corrosion on one causes all the current to flow in the other.
They make replacements.

The 2G was also known as the "Ford Fire Starter", because of that idiotic connector.
The 3G uses a single stud with nut.
 
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Blown88GT

Founding Member
Nov 13, 1999
2,144
505
164
Palm Beach Gardens, FL
I have continuity on the green/red all the way to the plug at the instrument cluster. The circuit on the instrument cluster has continuity. There is 12v present at the alternator with the key on. Light will not come on. What does the ignition side of the light do? Just provide the 12v? If so how can the light not come on? Resistor bad?
p.12 of manual (p.15 of pdf)
 

SHOme

Active Member
Nov 16, 2018
63
40
28
51
Maryland
Fixed it was the connector going to voltage regulator. It looks fine but when I replaced it everything worked as it should. Pulled instrument cluster for no reason. So in the trouble shooting guide I would recommend an amendment for rookie troubleshooting. If the battery light is not working but you have power to the lt green/red wire at the voltage regulator try jumping the wire to the regulator and see if light comes on. This would have saved time on the instrument cluster and had me back on the road quickly. Maybe I just didn't understand the write up and most electrical minded folks would have done this. Thanks for the help again. I'm sure I will need it in the future.
 
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