Alternator polarity?

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MOA

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1972 dart.
I bought a new Alternator from rock auto, slapped it on there. It smoked one of the field wires. Flipped the field wires around, seemed to be ok.

I connected exactly like the old one.

Put old one back on, no problem. Only reason I replaced it is because it is very old and dirty.

How do you reverse the polarity?
 
It would appear that you have a square back 2 field wire alternator, Correct?

I would disconnect the 2 field wires and check both field wires to the case of the alternator with an Ohm meter, you should have no connectivity from the terminal to the case. test each terminal to case seperatly.

My gut says that one of the terminals is grounded (shouldn't be for a square back 2 field wire alt)
 
Continuity test beeps on both field terminals.
Positive to field, no beep.
Field to body.
 
You have the "rebuilder's surprise." Somebody oughta sue the **** out of those people. Here is what you have. A 50-50 chance. The isolated field units whether squareback or round, have TWO field terminals and they are supposed to BOTH be isolated from the case/ ground. Those are 70/later and one goes to switched power, the other to the VR

So if you get "lucky" and hook the ungrounded one to the blue (power) it will just overcharge........like a *****..........but if you are unlucky and get the blue hooked to the grounded one, you can smoke some wiring.
 
both field terminals should have infinite resistance ( large numerical ) from terminal to case with wires removed. 0.000 Ohms is the same a dead short.

if you have a digital volt Ohm meter set it to Ohms and with wires removed touch the case with the plack lead and touch one of the field terminals with the red lead what reading do you get?
 
Lucky I didn't smoke the whole system.

I'm less than a week from being on the road, having to re wire the whole thing would of been discouraging.

I need tire smoke, not wire smoke. Faaakkk
 
this might not be exactly your car (wire colors might be different) but what you basically have

upload_2020-6-27_18-25-52.png


The Alternator you should have (square back, 2 field wire)
upload_2020-6-27_18-42-15.png


The Alternator you probably have (square back, single field wire)
upload_2020-6-27_18-52-7.png




What you don't have (round back, single field wire)
upload_2020-6-27_18-47-6.png


I forgot to mention that the 0.5 ohm number is just my best guess of the resistance the field coil would have, but you get the idea
 
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That would f-d up if they supplied a squareback with one field grounded.

Most a-bodies (ignoring Leece Neville and other rare options)
Through 1969 Model year. "Round Back" with one insulated terminal and one brush uninsulated and grounded to case.
1970-1971. "Round Back" with both field terminals insulated. Uses Regulator with triangular connector plug.
1972-76 "Square Back" with both field terminals insulated. Uses Regulator with triangular connector plug.

Dana - your illustrations got out of sequence.
 
If you kept the old one, you can pretty much clean and service it yourself.

As far as the smoke. its also possible the smoke you saw was harness wiring related. clean the exposed wires - any bad insulations? How about the connector? How does that look? Might have to remove the housing from the terminal to see if the wires are good.
 
1972 dart.
I bought a new Alternator from rock auto

Not quite—you actually bought a "remanufactured" alternator. "Remanufactured" parts are notorious junk.

If you want a real new alternator, an item made by Chrysler with good components and not "remanufactured" by untrained apes using cheap Chinese component-shaped trinkets in a dirt-floor factory,* you can buy one quite reasonably from Old Car Parts Northwest; they've got scads of 'em on the shelf. New genuine Chrysler regulators, too.

When you go to hook it up, there is no polarity involved; either field wire can go on either field terminal with no advantage either way around.

*-No exaggeration.
 
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You have the "rebuilder's surprise." Somebody oughta sue the **** out of those people. Here is what you have. A 50-50 chance. The isolated field units whether squareback or round, have TWO field terminals and they are supposed to BOTH be isolated from the case/ ground. Those are 70/later and one goes to switched power, the other to the VR

So if you get "lucky" and hook the ungrounded one to the blue (power) it will just overcharge........like a *****..........but if you are unlucky and get the blue hooked to the grounded one, you can smoke some wiring.
One of my field wires got grounded accidentally to the case and fried up pretty bad taking some other wires with it in the harness.
So this what I ended up with after inspecting my wires. At least now I know my wiring is good. I feel the pain Lol!
20181229_194755.jpg
 
need to get the right wire to replace that section.

What gauge is it?

I'll probably go to a one wire gm alt in 6 months or less.

I have a brand new Optima battery, don't want to mess it up.
 
First "rebuilder's surprise" I remember finding was in the '80's I worked for a local parts store. Guy had a Dodge pu, and came in with the rebuild on the truck "How come it seems to be overcharging all the time?" So he was lucky........just happened to hook the blue to the ungrounded terminal.
 
I noticed, whoever rebuilds Napa alternators locally here, cuts that spade connector, so u cant plug it in on this roundback.
Screenshot_20200627-221418_Gallery.jpg
 
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I noticed, whoever rebuilds Napa alternators locally here, cuts that spade connector, so u cant plug it in on this roundback.View attachment 1715552290
:rofl:
Presumably you unwrapped the harness to get that out.
That should be the smallest wire, but make sure there is no damage on the rest of the circuit going back to the battery.
I'd be most concerned about the column connector, and other connectors in between.


need to get the right wire to replace that section.

What gauge is it?

Look at the wiring diagram in the '72 shop manual.
The letters next to the wire will be something like J2A 18DBL. That translates
Run (Ignition 1) circuit. 2nd section branch A. 18 ga Dark Blue
I know the earlier cars, it was typically 18 ga for A-bodies and 16 ga for B-bodies. '72 might be the same.

Here's what I'd recommend:
Buy a couple feet of Blue insulated GXL from Wirebarn.
Get a new Chrysler type terminal and an open barrel terminal crimper.
Put this terminal on the end of the new wire and transfer the original plastic housing.
example here
Get an open barrel splice terminal and heat shrink tubing.
Splice the new section to the original in the harness.
Shown here:Inline wiring splice clips........from the Dodge RAM service manual
Some alternative methods Clever splice
Rewrap the harness.
Done and it will be as good as new.

As far as the alternator.
if your place will take it back/exchange the bad one, do that.
Take your old one and clean it.
Take out the brushes and replace them, along with the insulators and insulating washers, if needed.
Brush ID: Alternator repair, a little show and tell.
If it spins well - no looseness or tightness - run it.

On the bad one if they won't take it back.
Open it up and trace down where the field circuit is grounding out.
Its either a brush or terminals grounding, or the rotor is grounding.
If its the brushes and terminals, replace them.
If its rotor related, that will be a more difficult repair. We can help you tackle it or you can find a small shop to deal with it.
Replacement of a rotor involves removing and reinstalling the pulley. Write up or guide available for alternator pulley install?

Another thing to check when the alternators are open.
Output terminal (big stud) is tight and and straight. It can only be tightened when the cases are apart.
It is also critical the stud is insulated from the case!
 
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PS. Rockauto will prob exchange it. They exchanged a bad AC Delco 12Si I had on the jeep for three or four hundred miles. Problem was a miscast or misdrilled insulator for the output stud. So much for OE quality.
rolleyes-gif.gif

If so, do what I did when the replacement showed up. Check it out first!
Also never exchange your old unit - especially if its still working. These days we need backups for the crappy replacement parts. :realcrazy:
 
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Look at the wiring diagram in the '72 shop manual.
The letters next to the wire will be something like J2A 18DBL. That translates
Run (Ignition 1) circuit. 2nd section branch A. 18 ga Dark Blue
I know the earlier cars, it was typically 18 ga for A-bodies and 16 ga for B-bodies. '72 might be the same.
Here's that circuit connection to the battery based on '73. A '72 v8 Calf car would be similar.
upload_2020-6-28_9-32-18.png
 
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