Not charging, need wiring verication

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Apr 1, 2021
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Hello all, My son and I are finally driving the 72 Coupe! Everything seems to be working well apart from my charging. I am looking for a little sanity check to verify if I have the regulator connector wired properly my schematic does not have the F S A I on the regulator diagram so I went left to right on the connector so Blue Orange goes to (F)White Black goes to (S) Light Green Red goes to (A) and Yellow White goes to (I) along with the suppression capacitor.

I have 12.43 V when the car is running and it drops to 12V when lights, blower are on. Doesn’t waver when I rev the engine either. I also don’t have a warning light for the Alt idiot light, but that could be a bulb.

I am attaching a picture of my regulator as wired and the alternator as wired.


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For future info, we have wiring diagrams available on this site. In the 7173 Wiki at top of the forum’s home page, you can locate the wiring diagram by the model year.
So, things are not as well as hoped. I am still having charging issues. If I run my wiring as layed out in the factory schematic found here it charges however, it also drains the battery overnight. the confusion is related to the yellow white and the green red on Connector C4 to the regulator. I have several schematics, and they show different configurations. for those 2 wires. Highly frustrating.

71Fast has been helping me with great schematics, but suggested I pose the question here.
Can you post pics of that area? It will help, the regulator and the back of the alternator. I’m not sure the situations are linked, in my humble experience. You could have a parasitic drain and it not include the charging system. But, using the wiring/diagrams, you can test the regulator for shorts/grounds, if you suspect that is the source. The best way I’ve found to find that loss is to disconnect the ground at the battery, connect in series a test light, and start by removing one fuse at a time to see if the light goes off. If none of the fuses do that, then you’ve isolated the loss within the primary power feeds. That’s where I would start.
Thanks for the reply and troubleshooting suggestion, good idea.

I am attaching a picture of the way my C4 is currently wired. Alternator is new and as of yesterday a new regulator is installed. The photo shows my green red and yellow they way they were when charging and they are now swapped.


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Hi, it might be a couple of issues. One thing I noticed on your the picture was bare wire exposed on the yellow/red wire. The insulation tends to shrink and pull back. On my car I had issues with charging due to age of the harness/blade connectors to and from the alternator. You can get a replacement harnesses if needed.

I also think that 14V volts is more the correct charging voltage needed at battery at a certain RPM. Somebody correct me if wrong.
Your wires are in the wrong slots on the plug, looks like someone swapped the Lt Green/Red stripe with the Yellow/White stripe


There are two configurations for the voltage regulator plug - w/warning lights and w/gauges. The '72 diagram calls out which wires are present in each configuration. The Orange/Lt Blue and Yellow/White are always in the same position. The Lt Green W/Red moves depending on the gauge package.



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I already mentioned they were wrong in the photo….

the “somebody” was me because I was trying to match the factory diagram. Like I said, in the wrong configuration (as shown) it charges. If I do it the correct way it does not charge. Rest assured it’s correct now.

If you are wondering what led me to swap connectors to begin with see the attached photo. It shows it exactly the same as the one you posted.


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I understand where your wiring order came from, which is why I posted the connector configurations.

My first step now would to ensure I have a clean battery to apron to block ground path, and that the regulator is as well.

Next, I'd hook up a voltmeter and full field the alternator through the A and F terminals on the regulator connector for just a few seconds. You should see a sub-15V output. If not, then either the harness is bad or the alternator is. At that point, I'd bring it back to the parts store and have them test it.

If you get more than 15V, the alternator is junk, return it.

If you get a 13.5v ~high 14v reading, then it's good and the regulator is the issue

New parts do not always equal good parts.

IMO, I'd swap that harness at the earliest convenience for a new one from your favorite vendor.
I already mentioned they were wrong in the photo….

the “somebody” was me because I was trying to match the factory diagram. Like I said in the wrong configuration(as shown) it charges. If I do it the correct way it does not. Rest assured it’s correct now.

If you are wondering what led me to swap connectors to begin with see the attached photo. It shows it exactly the same as the one you posted.
If it charges in the wrong configuration, are you sure you have the correct harness? The configuration depends upon whether you have an ammeter (or voltmeter) or an alternator indicator lamp. The alternator harness and voltage regulator wiring must correspond to either of these 2 configurations. If the configuration is incorrect to properly charge, then you have a major mis-wiring issue.
At this point I am really at a loss. I appreciate all the advice guys! I have to work away from home this week so I will revisit the issue when I get back. I have the warning lamp. Full gauge package to include tach is down the road. I will have to do it all over again when I do.
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Ok with taking everyones suggestions, verifying and Ohming wiring, replacing alternator( it was bad out of the box) replacing regulator I still don’t have a charge. Now, one thing that I am thinking is the ignition switch is out of a ‘73. There are 2 different part numbers for 71/72 and 73. Could this be the culprit? Hard to tell from schematics what’s going on internally.
Charging with stock wiring on a 7173 is straightforward. There's one lead to the alternator harness to excite/initiate the voltage regulator. If you have the proper alternator harness, then a no-charging situation is due to either mis-wiring the alternator, a bad alternator, no continuity on the alternator to starter solenoid battery post, or a bad voltage regulator.
I just recently bought a 72mach1, that was wired all wrong, as stated before, on the regulator, the orange blue wire is the field wire to the alt, check with volt meter, with key off, it should read 0 volts, turn key to on position, should read battery voltage, found on my car that the alt harness was wired wrong, was seeing key voltage thru stator wire, also ensure neg battery cable is grounded to frame, also ensure good ground connection on voltage regulator. Once I did that, had 14.25 at battery while car was running
Frame ground and ground for the regulator reads 0 Ohms. Measured from negative battery terminal to frame and to regulator case. I have constant 12V on the yellow wire on connector C4 ( A terminal)

F terminal which is orange/ light blue is the field wire and does not have 12V on it key on or off.

I have ohmed the white black, black orange and red blue to the alternator and all read 0 Ohms from terminal to terminal.

Voltage regulator is new as was the one I pulled off.

What wire provides the switched 12V to the regulator? with the yellow white being constant 12V and everything else running directly to the alternator I can’t see how it would get switched by anything.

I can‘t even begin to convey my frustration at something that is so simple.
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The switched 12V should be the green/red wire. Why are you not mentioning it in your description? It connects the main headlight harness to the alternator harness and feeds the voltage regulator.