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Battery overcharging 15.3-15.6V

JG1966

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My battery is charging at 15.3 to 15.6 depending on rpms. I am a newbie to electronics and some of you guys are brilliant. I need help. I did research on site and ran some tests. I unhooked the field wires at the alternator and battery did not charge (I believe that means alternator is good). I didvoltage drop from battery negative to voltage regulator case. Got .00 to 01V. I have good grounds from battery to engine, battery to radiator frame, engine block to firewall and engine block to frame.
These are some numbers. If any of them look wrong (after first two, obviously), please let me know
1. Battery post to post (car off) 12.6V
2. Battery car idling to 1500rpm 15.3-15.6V
3. Alternator power wire stud 15.5 at idle
Now, I'm not sure when I test blue and green wires at alternator if I go to field wires and to ground or if I go one to battery positive and other probe to field wire (and not sure if I'm supposed to probe from back with wires still on alternator or if I'm supposed to disconnect from alternator and probe into the connector from the front).
So here it is (all these with car running)
1. Battery positive to green field wire connected to alternator 6v (bounces between 6-0.5v)
2. Battery positive to green field wire disconnected from alternator 13v (bounces around between 13-2v)
3. Battery positive to blue field wire connected to alternator 1.40v
2. Battery positive to blue field wire disconnected from alternator .96v
I know this is confusing but any help would be great.
 
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“3. Battery positive to blue field wire connected to alternator 1.40v”

That is the issue, needs to be less than .5 volts. It’s resistance at connections/wiring in the Ighition1 circuit. Assuming the avatar picture is the vehicle involved, check for corroded bulkhead Packard connectors on the blue/white trace wires, and the Molex connectors for the ignition switch, both red and blue wires.
 
“3. Battery positive to blue field wire connected to alternator 1.40v”

That is the issue, needs to be less than .5 volts. It’s resistance at connections/wiring in the Ighition1 circuit. Assuming the avatar picture is the vehicle involved, check for corroded bulkhead Packard connectors on the blue/white trace wires, and the Molex connectors for the ignition switch, both red and blue wires.
Thanks 72. Yes, avatar is car involved. I'll check connectors. Dumb question. Do I check for ohms or voltage drop?
 
Voltage drop while running is more accurate to pin down just where the issue is. Battery post to each side of the igh switch Molex terminals, then each side the bulkhead terminals. If the wiring is stock, connection issues should be obvious on inspection. Don't forget to inspect the bulkhead terminals in the charge circuit as well.
 
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Voltage drop while running is more accurate to pin down just where the issue is. Battery post to each side of the igh switch Molex terminals, then each side the bulkhead terminals. If the wiring is stock, connection issues should be obvious on inspection. Don't forget to inspect the bulkhead terminals in the charge circuit as well.
I looked at the blue wire to the bulkhead in engine bay, removed it and cleaned it, visually inspected bulkhead under dash and looked at Molex terminals. Didn't see anything obvious. I did voltage drop test, from battery positive to blue wire bulkhead connection and got .78-85v when I stuck prong in. I'll need longer wires to do voltage drop test under dash. If voltage drop is .78V
testing from firewall, does that mean problem is somewhere along circuit inside the car? And does it mean it's definitely the blue wire? Is there an easy way to confirm the voltage regulator is good?
 
My battery is charging at 15.3 to 15.6 depending on rpms. I am a newbie to electronics and some of you guys are brilliant. I need help. I did research on site and ran some tests. I unhooked the field wires at the alternator and battery did not charge (I believe that means alternator is good). I didvoltage drop from battery negative to voltage regulator case. Got .00 to 01V. I have good grounds from battery to engine, battery to radiator frame, engine block to firewall and engine block to frame.
These are some numbers. If any of them look wrong (after first two, obviously), please let me know
1. Battery post to post (car off) 12.6V
2. Battery car idling to 1500rpm 15.3-15.6V
3. Alternator power wire stud 15.5 at idle
Now, I'm not sure when I test blue and green wires at alternator if I go to field wires and to ground or if I go one to battery positive and other probe to field wire (and not sure if I'm supposed to probe from back with wires still on alternator or if I'm supposed to disconnect from alternator and probe into the connector from the front).
So here it is (all these with car running)
1. Battery positive to green field wire connected to alternator 6v (bounces between 6-0.5v)
2. Battery positive to green field wire disconnected from alternator 13v (bounces around between 13-2v)
3. Battery positive to blue field wire connected to alternator 1.40v
2. Battery positive to blue field wire disconnected from alternator .96v
I know this is confusing but any help would be great.

https://www.forbbodiesonly.com/moparforum/threads/how-my-charge-system-works.184522/
 
The total measured voltage at the battery is the regulator reference voltage plus whatever voltage drop between the battery and the ignition1 blue wire at the regulator. 15.6v - 1.4v = 14.2v, sounds like the regulator is good. If you are measuring a .8v drop at the blue/white wire connector at bulkhead, sounds like you may have additional drop in the engine harness somewhere as well. Need to reduce the total voltage drop as low as possible. Common spots are bulkhead connections, ammeter connections, ignition switch and or the ignition switch Molex connecters mentioned.

If you want to rule out the regulator, temporarily and carefully jump the blue wire connection at the regulator to the positive battery post. The then measured charging voltage is the reference voltage of the regulator.
 
The total measured voltage at the battery is the regulator reference voltage plus whatever voltage drop between the battery and the ignition1 blue wire at the regulator. 15.6v - 1.4v = 14.2v, sounds like the regulator is good. If you are measuring a .8v drop at the blue/white wire connector at bulkhead, sounds like you may have additional drop in the engine harness somewhere as well. Need to reduce the total voltage drop as low as possible. Common spots are bulkhead connections, ammeter connections, ignition switch and or the ignition switch Molex connecters mentioned.

If you want to rule out the regulator, temporarily and carefully jump the blue wire connection at the regulator to the positive battery post. The then measured charging voltage is the reference voltage of the regulator.
Thanks 72. I would like to rule out the regulator. In the FSM it says "Connect the positive lead from a voltmeter to the ignition Number one (1) terminal of the ballast resistor."..... Does that mean I unplug ballast resistor and connect lead to it or do I leave ballast plugged in and stick probe in back? Thanks
 
Leave things connected and under load when doing voltage drop tests.
Thanks 72. I ran FSM test on voltage regulator. Got 14.4V on relatively cold engine, which means regulator is good. I'll recheck bulkhead connections and ignition switch Molex connecters, and take a look at ignition switch (I never got to that yet) . My ammeter connections are bolted together and covered (I did the MAD bypass long ago). Thanks
 
Thanks 72, my head is spinning from looking at these wiring diagrams. I have two questions.
1. You said to "inspect the bulkhead terminals in the charge circuit." What is the charge circuit (what color wires)? Is that the wire from the battery/starter relay with the fusible link?
2. Are any of the wires/connections that could be giving me issues going through the fuse box or only the bulkhead connector/molex connectors?
Thank you again for all your help.
 
I had a new voltage regulator which i purchased @ O'rielys tested, before i installed. 15.5, threw it in the trash can. just for thought
Thanks Goldmyn. I tested my voltage regulator and it was right on.
 
Sorry to hear that!
Ok. This might be a clue. When I test for voltage drop from battery positive to blue wire at alternator with key on, I get 1.32V volts. If I unplug the voltage regulator, it drops to .72V. Does that narrow anything down?
 
Fast check take a ohm meter and between the pins on the voltage regulator should be between 1 and 3 ohms.
 
Fast check take a ohm meter and between the pins on the voltage regulator should be between 1 and 3 ohms.
I just did that. It blinked once in the mid 100s (135, 167, 184) and then went out. I retouched and got another reading in the mid 100s.
 
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