'83 D150 overcharge

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mwd782

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Hello.
My 83 Dodge has an overcharge issue. At the alternator it's showing 12.6 at the pin (black wire) 12.0-12.2 at red field wire and no voltage at green field wire. I'm guessing the green wire is grounding out and that's causing the issue. Anyone know how I fix this?
 
Wow that's a loaded post.


Over charging is too much voltage.

Your describing and no charging situation.


Is your 83 have a standard 60s 70s style isolated field alternator?

If so ..

If you have 12v at one field wire and 0 volts at the other field wire that sounds more like an open field to me. If the 0v was grounded that would cause a full field situation causing 17+ volts if charging.

With 0 volts there is no voltage getting through the field coil in the alternator.

Some easy tests.

Pull the green field wire off the alt.

With the key in Run, check for 12v on the red wire terminal AND on the terminal you took the green wire off of. It should read 12v on both.

Another test would be to momentarily ground the terminal you took the green wire off of and check charging voltage it should be high like 16 to 18v don't leave it this way long and turn off as much electronics as you can before hand.


If your alt is NOT AMa 60s 70s style fo not donas I have described till you know what each terminal does
 
My description was a bit off I'll add more detail. At the post the charge keeps rising up to 18volts when truck is on. The red wire terninal has a charge .4 to .6v lower than the post and the green wire terminal has no charge. So an open field situation as you described
 
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If the green wire is touching ground, then that's all you need to know. That's very bad as its full fielding the alternator. Find where its getting pinched or touching ground.

if its not that obvious how 'bout throwing a few pictures up since the wire colors are a bit different than the 70s cars. Alternator and its connections. Regulator and its connector

What's the ammeter show when the engine is running?
At work our '87 dump still had the ammeter.
The ammeter is showing battery charging or discharging.
That is another clue.
 
I believe the difference is that the red wire is a blue wire on other vehicles. My black goes from post to battery. Red(Blue) from alt to VR and ignition switch/ballast resistor/ECU and fuze holder. Green wire from alt to VR. I've got no voltage on the green wire. When engine is running voltage keeps rising on alt overcharging battery. I'm on voltage regulator #4 with a vintage Mopar one on the way.
 
Holy crap you’re hard to follow. Post pics of your set up. Start there.
 
I've redone the wiring here. Blue wire goes from VR to ignition and alt (red wire at alt). Green wire from VR to alt (black with pink at alt). My issue is that the green wire has no voltage. Causing alt to rise in voltage when engine is on.

IMG_20250612_194950461.jpg


IMG_20250612_194931750.jpg
 
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Ask yourself this:
When something like a light bulb or motor is turned on, what's the voltage at the grounding wire?

1749817107918.png
 
The next question is what is the voltage at the regulator's sensing terminal ?
If the wire to the sensing terminal has been cut, or there is voltage drop before it gets there, then regulator is doing what its set up to do.
 
Sensing wire has about a .2 to .4 voltage drop at the regulator. That's the issue I've been chasing replacing most electronics between.
Is there supposed to be voltage coming out of the green field wire at the regulator? If there isn't is this caused by the voltage drop?
 
How these work.

The "run" circuit, feeding power to the ignition, also feeds power to the blue wire to the VR (sense and power) and also to either field, evidently red in your case.

The VR controls "the amount of grounding" on the green wire. I believe it is pulsed.

This is similar to many solid state switching circuits, where a transistor is switching a ground leg of a circuit.

You MUST determine if there is a short in that circuit, easy.

Turn the key to run. Measure The red to ground and the green to ground right at the alternator, with all wiring connected normally

The red should be close to "same as battery," and the green should be quite low. This shows that the VR is getting power, that the field is getting power, and that the VR (or a short) is pulling the green side of the field to ground, causing it (properly) to draw current

Pull the connector off at the VR. Measure the green to ground at that point. The voltage should be same as battery. Again, with all other wiring connected, with the key still in "run."


As a double check, just check continuity --- With field wires unhooked, you should show low resistance between the two field terminals and open/ infinity from either field terminal to ground

If that checks OK, then with the green unhooked at the VR and the alternator field, check the green wire for continuity to ground, which should be open

THE VR MUST BE grounded. Scrape around the mountings and use star lock washers

As a last double check, with the engine running and charging, you should be able to either disconnect the green field wire at the alternator, or disconnect the VR connector, and either action should stop charging, output should drop to 12.6 or a little more because of "float"

If these tests check out and you have verified that the VR is in fact grounded, replace the VR
 
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mwd782 said:
Sensing wire has about a .2 to .4 voltage drop at the regulator. That's the issue I've been chasing replacing most electronics between.
Click to expand...
Depending on how this has been checked, in general .2 or .4 V difference is not a problem.

mwd782 said:
Is there supposed to be voltage coming out of the green field wire at the regulator? If there isn't is this caused by the voltage drop?
Click to expand...

You have to answer the question in post #8 and then the rest will make sense.
 
Mattax said:
Ask yourself this:
When something like a light bulb or motor is turned on, what's the voltage at the grounding wire?
Click to expand...

When lights on ground has no voltage.

67Dart273 said:
Turn the key to run. Measure The red to ground and the green to ground right at the alternator, with all wiring connected normally
Click to expand...
Batt 12.2v
Red 11.8v
Green 0v

67Dart273 said:
Pull the connector off at the VR. Measure the green to ground at that point. The voltage should be same as battery. Again, with all other wiring connected, with the key still in "run."
Click to expand...

Green at alt 0v


67Dart273 said:
As a double check, just check continuity --- With field wires unhooked, you should show low resistance between the two field terminals and open/ infinity from either field terminal to ground
Click to expand...

Unhooked no voltage at both terminals

67Dart273 said:
THE VR MUST BE grounded. Scrape around the mountings and use star lock washers
Click to expand...

Scraped and grounded with extra ground wire added.

67Dart273 said:
As a last double check, with the engine running and charging, you should be able to either disconnect the green field wire at the alternator, or disconnect the VR connector, and either action should stop charging, output should drop to 12.6 or a little more because of "float"
Click to expand...
Battery reads 13V and is slowly dropping.

Thank's for all the help. Much appreciated from a newb.
 
mwd782 said:
When lights on ground has no voltage.
Click to expand...
Exactly.

So when current goes through the rotor - which is an electromagnet - the voltage coming out is for all practical purposes zero.
The green wire goes to the VR, and the VR controls the connection to ground. When its connected to ground the electromagnet is at maximum strength. If the grounding is happening at the VR, then the VR is broken or the VR is seeing very low voltage.

One test would be to unplug the VR. If the alternator is still full fielding then there is a short to ground in the wiring or at the alternator.
 
When the VR is unplugged battery sits at 12.4v even after acceleration
 
That seems to confirm the problem is either in the regulator, or the regulator is not sensing the battery voltage.
I found a '79 truck diagram on mymopar and it shows the feed to the rotor and the sensing wire for the regulator were welded together at a big splice. No idea if that's true on your '85
1749860225768.png



67Dart273 said:
As a double check, just check continuity --- With field wires unhooked, you should show low resistance between the two field terminals and open/ infinity from either field terminal to ground
Click to expand...

mwd782 said:
Unhooked no voltage at both terminals
Click to expand...

When he wrote continuity check, that means set the meter to ohms (or continuity). Turn the power off, or if needed disconnect the battery. Then measure for resistance or connection between the two locations.
 
Almost same wiring yes. Here's a shot from the manual.

Mattax said:
When he wrote continuity check, that means set the meter to ohms (or continuity). Turn the power off, or if needed disconnect the battery. Then measure for resistance or connection between the two locations.
Click to expand...
No continuity between the two field terminals metre doesn't move . Set at 20k on ohms.

IMG_20250613_175011220.jpg
 
mwd782 said:
No continuity between the two field terminals metre doesn't move . Set at 20k on ohms.
Click to expand...
H'm.

The alternator works, we know that.

Try a lower setting. Touch the probes together and that will show the zero. On analog meters often the needle can be adjusted so its on zero for that scale.

With the brushes removed the resistance should be just a few ohms. Maybe 1.5 to 2 ohms on a revised square back. Through the brushes it will be higher, maybe 5 ohms.

Then what he was looking for was a circuit issue inside the alternator.

First measure across the terminals
1749863422603.png


Then check to see if somehow the one of the terminals is shorting to the case
1749863492199.png


1749863547197.png
 
Put it on 200 setting as low as it goes. Touched both terminals reads this. Same thing with each terminal to the ground on the alternator the truck body or case of alt.

IMG_20250613_182118744.jpg
 
You've been given good diagnostic advice so far and it’s nice to see you following it. I’ll add only one thing I haven’t seen suggested yet. @67Dart273 briefly touched on it in post 11 but it was an only a brief statement. Before you do anything else, make sure the VR is cleanly grounded to the body. Remove it, sand the body to bare metal at the contact points, and re install it with star lock washers. It’s also necessary some times to run a ground wire directly to the battery neg from a mounting bolt on the VR. It HAS to have a good clean ground.
 

Between the bolt and the VR is fine. You can measure the voltage drop from the VR body to battery ground and it should be 0.0v
 
mwd782 said:
Any idea why? Alternator not grounded?
Click to expand...
Open = not connected.
Your saying (as I understand it) that when you touch the probes together its showing
1 .

It should be showing 0.0 or 0.1 or 0.2

What's it show when the probes are touching?
 
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