Alternator Troubles! 1973 Plymouth duster 318

[CrazyBlaize]

Hey yall, I've Been slowly working out all the electrical gremlins in my car for the past year, and I have 2 big ones left. but as of right now, id like to figure out why my alternator isn't charging, the main Wire (I don't know the correct names of these Wires) reads a constant voltage from the battery and slightly drops when under load (E.I putting the key in the ON position) but the BLUE and GREEN wires (Field wires?) show no voltage what so ever.

so here's my main question; Where do I start?

I have a brand new alternator in the car now just for preventative maintenance, which I tested in another vehicle and is working fine. and I have good quality wire on hand if I need to run some new ones, but I don't even know where to start when it comes to that.

I really appreciate everyone's time and will be watching this thread religiously, so don't be afraid to throw down some knowledge, I'm only 20 and have a good but limited knowledge when it comes to electrical systems in these A-Bodys, so I really do appreciate anything I can get.


Thanks!
Blaize

 

[Dana67Dart]

@67Dart273

 

[CFD244]

@67Dart273

 

[Dana67Dart]

In a nut shell, you appear to have a isolated field alternator.

The voltage regulator regulates the ground side of the field cir.

One of the 2 field wires supplies a constant 12 (nominal) volts.

The other supplies a variable ground.


The fact that you have 0 volts on both wires suggests that the constant feed wire is not supplying the required 12 V

That is where I would start


Now for the required...

Go to mymopar.com and download your cars or the closest to your cars year Factory Service manual.

There are also electrical schematics there as well .


Watch this video.

 

[superchargeddrt]

Here's how I wired mine up. The relay is in there to eliminate the flickering headlight syndrome. This is typically caused by dirty ignition switch contacts. If you don't want to use the relay then just connect the blue wire that is coming from the ballast resistor directly to the I (ignition) terminal on the regulator and then over to one of the field brushes on the alternator. The green wire goes from the regulator to the other field on the alternator. Hopefully this helps you.

 

[Mattax]

Hey yall, I've Been slowly working out all the electrical gremlins in my car for the past year, and I have 2 big ones left. but as of right now, id like to figure out why my alternator isn't charging, the main Wire (I don't know the correct names of these Wires) reads a constant voltage from the battery and slightly drops when under load (E.I putting the key in the ON position) but the BLUE and GREEN wires (Field wires?) show no voltage what so ever.

The main wire is the alternator output wire. It is connected to the battery output wire and the main circuit feeds.
On a standard circuit these are all joined at a welded splice. On a car with a rear defrost grid, or fleet high output alternator, its split up a little.

The blue field wire is a part of the ignition run circuit. One branch goes to the voltage regulator - which can be considered the 'sense' wire. Another branch goes to the alternator to supply power to the rotor.
It and the green field wire are explained here: Identifying Chrysler Alternators (1960-1976)

so here's my main question; Where do I start?

Start with the linked post about alternators.

When done with that, your job will be to trace back the blue wire to find out where the break in the circuit is.
Green wire will not have power unless the blue wire has power.

 

[67Dart273]

OP first thing you do if you have not is wander over to MyMopar.com and download the factory service manual, free, and also the third party wiring diagrams. Those are zipped, and you have to extract them and pick the correct one

If you look at the diagram already posted, the key switch "run" line, IGN1, comes out into the engine bay, and branches off and feeds the ignition, the alternator field, the VR IGN terminal, electric choke if used

DID YOU MODIFY the ignition system, ballast resistor, or is the wiring in that area up near the bulkhead connector and ballast resistor ----is that modified or damaged?

 

[Mattax]

When done with that, your job will be to trace back the blue wire to find out where the break in the circuit is.

This will get you started. Your car and the diagrams in the shop manual will provide the details for tracing back.

 

[supertruck]

Just for thought - print the wiring schematics and then get a long piece of cardboard and tape the schematics to it, in order. Makes following the flow of the wires much easier. You can fold it up when not in use. Believe me, you'll use it a lot.

 

[CrazyBlaize]

Thanks for all the awesome replies!

so far, I've been able to get constant voltage to the blue field wire, I needed to redo the connection to the ballast resistor, but here's my next obstacle, BOTH field wires are reading 10volts with the ignition on, from what I've seen online that doesn't seem to be quite right? I know the green should be seeing a lesser voltage. on my way now to get a voltage regulator to see if that changes anything.

ALSO: there is continuity between the blue and green field wires on the alternator when the ignition is both on and off. so, yeah? hopefully that means something.

 

[Mattax]

BOTH field wires are reading 10volts with the ignition on, from what I've seen online that doesn't seem to be quite right? I know the green should be seeing a lesser voltage. on my way now to get a voltage regulator to see if that changes anything.

ALSO: there is continuity between the blue and green field wires on the alternator when the ignition is both on and off. so, yeah? hopefully that means something.

Short answers:
10 Volts with ignition On = Battery charge is probably low, very low.
Both wires showing the same voltage: Those two wires are connected to each other and circuit down stream is open.
You also know from your continuity test that the wires are connected to each other, and from your reading you know that they are connected through the brushes, slip ring, and rotor.

 

[Mattax]

Long Answers and follow up steps.

Battery: 10 volts with the starter turning is acceptable. 10 Volts in run - which is very low load - is not.
Try this
a. Measure battery voltage with key off, door shut (dome light off), nothing on.
b. Measure battery voltage with low load such as dome light light on, then add loads such as parking lights and then headlights.

Normally a fully charged battery will have a potential of 12.5 to 12.8 Volts
Add a small load and it will drop just a little.

If the battery is low, and it has enough acid (assuming removable tops) so you can see the level, put the battery on a charger. If its a manually control charger, charge it at a low rate. 2 amps would be OK.


Field Circuit:
Here is what is happening when you observe the voltage is the same at two locations.
Voltage goes down only when the electricity does work. When there is no resistance, there is no work. Also when the electrons are not moving, there is no work.

[A small aside here, it always pays to take a look at the ammeter to help complete the picture. The ammeter will reveal if the electrons are moving to or from the battery. ]

As you know from the "Alternator ID" thread the blue and green field wires are connected through the rotor. A continuity test will just show they are connected. With the key off, a resistance check will give some indication of whether there is short or not.

With the key in run and the battery as source of power, the voltage regulator will be read system voltage as low. [The regulator wants system voltage to be around 14 to 14.9 V ] Therefore the regulator should be internally connecting the green wire to ground.
But if the green wire is not connected, or the regulator is not working or well grounded, then the circuit will be open and no current will flow. No flow = no work = no loss of energy level (voltage)

If its 10 Volts everywhere in the main circuits that are connected, no current is flowing.

Graphically, no connection to ground, everything on the battery side is at the same voltage.

Only when and where the electrons move through a device, a resistor, or a poor connection do they lose energy.
Going through the rotor most of the energy becomes and electromagnetic field.
If they are moving through a resistor or poor connection, then the energy is all given off as just heat.

Back to your situation.
Check that the voltage regulator is well attached to the body, and the battery has a body ground on the negative terminal.
Check the green wire is intact back to the regulator. You could do this with key off, remove the connector at the regulator and the green one on the alt. Then do a continuity test of the green wire

If you test with the key in run, see if the ammeter needle moves slightly toward discharge. No movement of the needle, then there are no electrons moving. it shouldn't move a lot, but with ignition switch on run, it should show flow to ignition ECU, coil, the alternator field, and maybe an electric choke assist or carb solenoid. 5 to 6 amps.

 

[CrazyBlaize]

GOT IT! it was a mix of, an old alternator, a bad voltage regulator, and worn-out connections, but some TLC and new parts did the trick!

 

[Mattax]

Old alternator may be worth fixing. The squarebacks are pretty easy to replace most of the parts on as needed.
A lot of new alternators have high draw rotors that result in short life for the votlage regulators.

Regardless. Put that battery on a charger.
Recharging a battery thats really low with the alternator is a good way to damage stuff (connectors, battery itself, sometimes the ammeter)

The ammeter needle should never be more than 1/2 way either direction for any length of time. That's about 20 amps. You can get away with that for a few minutes but not much more. Full scale each way is about 40 amps and that is danger for sure. Shut it down if it goes there.

 

[Mattax]

Here's what happens when 40 amps goes through the circuit.

Actually held up pretty well considering how long they were subject to that load.

On the left is a bulkhead terminal for the alternator output on a different car, mine in this case.

It saw 15 to 30 amps over the course of 20 minutes or so because I had to drive back to camp charging the battery using the alternator. Sometimes you have no choice.

Charging Battery with Alternator - Warning

We've discussed this here more than a few times. Usually about how easy it can be to cook the battery or overloading the charge wiring. Here's another reason. "Any attempt to charge a low battery by the alternator will result in stator windings burning out" ebay item # 222689173585 This is...

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