Hey Guys I'm having a overcharging issue on my 71 Scamp I've changed 2 voltage regulators,car is putting out 15.5 volts my question is with both field wires un hooked and with key on should both terminals have 12 volts,any advice Thanks Don..
Overcharging
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67Dart273
Well-Known Member
This "sounds" like a classic case of voltage drop in the harness or ground, a subject I've posted many times
To check this, get your voltmeter as close as you can electrically to the VR. The ballast resistor power, or the blue alternator field wire are two points. Don't disconnect anything, leave all wiring connected "normal." Put the key "in run" with engine stopped. Stab one probe into the battery POS post, and hook the other to the power at the ballast. You are hoping for a VERY small voltage, the lower the better. Anything over about .3V you need to look into
The functional path in a stock harness is battery...starter relay stud...fuse link....through the bulkhead connector (RED ammeter wire) through the ammeter, out the ammeter on the BLACK ammeter wire, to the WELDED splice.....and branch off to the ignition switch connector.......through the switch......out the switch connector on the blue "ignition run" line....out the bulkhead connector.......and to the underhood loads, that is ballast, VR, alternator field, and depending on year model, electric choke and one or two smog doo dads.
The usual suspects are the bulkhead connector terminals, the ignition switch and the connector
To check this, get your voltmeter as close as you can electrically to the VR. The ballast resistor power, or the blue alternator field wire are two points. Don't disconnect anything, leave all wiring connected "normal." Put the key "in run" with engine stopped. Stab one probe into the battery POS post, and hook the other to the power at the ballast. You are hoping for a VERY small voltage, the lower the better. Anything over about .3V you need to look into
The functional path in a stock harness is battery...starter relay stud...fuse link....through the bulkhead connector (RED ammeter wire) through the ammeter, out the ammeter on the BLACK ammeter wire, to the WELDED splice.....and branch off to the ignition switch connector.......through the switch......out the switch connector on the blue "ignition run" line....out the bulkhead connector.......and to the underhood loads, that is ballast, VR, alternator field, and depending on year model, electric choke and one or two smog doo dads.
The usual suspects are the bulkhead connector terminals, the ignition switch and the connector
67Dart273
Well-Known Member
GROUND The VR MUST be grounded and at same voltage as battery NEG. To check this, run engine at simulated low/ medium cruise RPM, and check first with all loads off, and again with lights, heater, etc, powered
Stab one probe into the top of the NEG battery terminal, and stab the other into the VR mounting flange. Again you are looking for a very low voltage, the lower the better, zero is perfect
Stab one probe into the top of the NEG battery terminal, and stab the other into the VR mounting flange. Again you are looking for a very low voltage, the lower the better, zero is perfect
67Dart273
Well-Known Member
Also check the VR connector. Inspect the terminals with a lamp for corrosion, a nd work it in/ out several times to scrub the terminals, and "feel" for tightness. One way to improve the body grounding (on a V8) is to look at the front of the pass. side head. Those same holes in the end of the head are next to the firewall, unused, on the driver's side. But a short "eye to eye" starter cable, and bolt to the head, and to the firewall, such as the master cylinder mounting stud
Thanks for responding i will check that today i checked the ground from the green wire at the voltage regulator it was 11.4 volts with key on.
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The previous series of posts sounds like a lot but are not! Read each post thoroughly and absorb them slowly. Harness issues are abundant on these 50+ year old cars, with who knows how many mods others may have done over the years!
One reason I always suggest replacing the harnesses. Seems expensive but! Think of the alternatives!
One reason I always suggest replacing the harnesses. Seems expensive but! Think of the alternatives!
67Dart273
Well-Known Member
That green wire IS NOT A GROUND. It goes from one terminal of the alternator field to the VR. It is the means by which the VR controls the alternator
67Dart273
Well-Known Member
HOW THIS WORKS (the voltage drop problem) Bad connections in the ignition harness are the root cause of voltage drop, and current flow caused by the normal operation of the alternator field/ VR and ignition system is what effects the actual drop.
The battery is getting charged and the VR is supposed to SENSE the voltage "same as" being right at the battery. But if there is a VOLTAGE DROP between the battery POS and the VR, then the VR will say to itself "hey the battery is low we must charge it." Let's say when you perform the drop test (one probe on the battery POS, other probe at ballast power terminal) you read, say, 1.8V. That means that the VR sensing terminal is sensing 1.8V LOWER than the battery
So the VR "sense" terminal "wants" to keep that terminal at 14V (13.8--14.2). If the terminal is 1.8 LOWER than the battery, that means the battery will OVERCHARGE by the amount of the drop. So if the VR is correctly maintaining 14V at the "sense" terminal, and you add the 1.8V drop, the battery will be running at 14V + 1.8 = 15.8V!!!!
The battery is getting charged and the VR is supposed to SENSE the voltage "same as" being right at the battery. But if there is a VOLTAGE DROP between the battery POS and the VR, then the VR will say to itself "hey the battery is low we must charge it." Let's say when you perform the drop test (one probe on the battery POS, other probe at ballast power terminal) you read, say, 1.8V. That means that the VR sensing terminal is sensing 1.8V LOWER than the battery
So the VR "sense" terminal "wants" to keep that terminal at 14V (13.8--14.2). If the terminal is 1.8 LOWER than the battery, that means the battery will OVERCHARGE by the amount of the drop. So if the VR is correctly maintaining 14V at the "sense" terminal, and you add the 1.8V drop, the battery will be running at 14V + 1.8 = 15.8V!!!!
To add to what 67Dart273 wrote, or to say it another way.
The regulator controls current flowing through the green wire to ground. When the rotor needs to generate a stronger magnetic field, internally a direct connection to ground is made. In other, a switch is closed.
The voltage at I determines whether the current flows through resistance, direct, or not at all.
If the voltage I is 13.0 Volts, then it will allow current through even though you are measuring 15.5 Volts somewhere else.
If you are measuring 15.5 Volts at the Alternator output stud, and 13.0 Volts at a connection on the blue wires (say the ballast resistor or the bulkhead), that shows there is resistance to the current flowing between those two points.
If you then take the positive probe and place it on the output stud, and the other on the ballast resistor, it will show the 2.5 volt drop assuming its all in the feed. if there is resistance is in the ground, then it will be less)
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Thanks for your input on this ,,tonight i decided to look at bulk head harness connections the middle bulk head connector i found the 10gauge black wire was burnt and looks not making connections and that wire, looks at wiring diagram direct toward alternator i will repair that wire hopefully that will get me on the right track...I'll let u know again Thanks..
You're getting there!
That wire will at times carry a pretty high load.
It will carry the current to run the ignition, the power the alternator's rotor all the time.
Then add on headlights, brake lights, heater fan, etc.
Plus, charging for however long it takes for the battery to get recharged.
If your '71 has a 10 gage wire, that's good.
The bulkhead connection is a 'Packard 58' type terminal. Do a search here and that will get you more info on them.
Not the best for carrying high loads.
One work around that I like is to add a parallel wire straight through the firewall. Use a grommet of course. A crimped ring terminal on the alt end and a smaller ring terminal on the inside. Connect it to the ammeter stud.
That provides an alternative parallel flow path.
A similar scheme was used on '73 A-bodies with optional 60 amp alternator.
It's a little more complicated. It looks like it was used in conjunction with electric rear window defrost option but I have yet to see an unmolested original. Only going here by the service manual.
I think the standard alternator output wire to the bulkhead was not used, but again I don't know for sure based on the diagram alone.
You got some good advice from '67 dart'. He forgot to add in post #2 that a large black wire is also connected at the welded splice. This wire goes thru the bulkhead connector and goes to the alternator output. The terminal connectors in the bulkhead are barely adequate for the amount of current the big red and black connectors have to carry. And adding to that, the old 35 Amp alternator might/likely have been replaced with a more powerful one over the years. Problem city.
Matt's second diagram shows the separate 2 wire harness for the hi-output alternators. Straight thru the bulkhead with no connectors. My memory thinks a round 5/8" dia. hole was drilled thru the firewall, a grommet sealed out the water, and the red and black terminals on the ammeter would fit thru the hole. Note that these 2 wires are always hot!!!!
Matt's second diagram shows the separate 2 wire harness for the hi-output alternators. Straight thru the bulkhead with no connectors. My memory thinks a round 5/8" dia. hole was drilled thru the firewall, a grommet sealed out the water, and the red and black terminals on the ammeter would fit thru the hole. Note that these 2 wires are always hot!!!!
Oops, I read the title and thought you were talking about a trip to the dealership service department! 
Yes fir sur
well after finding the bad 10 gauge wire in bulk head connector and a new mopar voltage regulator car is charging normal at idle 14.2 volts ..went for test drive this morning all good then once i punched it gauge pegged 18 volts ,the dropped back to 14 radio stopped playing....then all ok .short time later pegged and came to 14 volts im stumped for sure before finding burnt connection..car was charging 15.4 volts so that problem fixed tempted to replace Alternator.!
You have a classic situation where the alternator's rotor is getting unregulated power.
First things to check are that the alternator and regulator are wired correctly.
If the second brush terminal, or the green wire connectoed to it touch ground anywhere, then power to rotor is unregulated.
What is this mean?
It means the rotor will be creating a maximum strength electromagnetic field full time.
If everything is wire right and good, then the next is to check for voltage drop between the alternator output and the regulator's control connection. The closest places to measure that will be ballast resistor, then the alternator field, or the bulkhead. Back probe the terminals while the engine is running.
If the alternator is running at 14.2 and the regulator is seeing 13.5 or less, then resistance between them that's contributing to the problem.
Instead of measuring voltage above ground, another way is to measure the drop direct. Put one probe on the output stud and the other probe on the terminal in question. Then you know the drop is in the wiring not the ground connection.
At 15.4 Volts, current is flowing to the battery - but its OVERCHARGING.
At minimum, it will cook off the acid in the battery.
Second, if the battery was low on charge to begin with, its going to draw an enormous load through the wiring. This is a good way to damage all the terminal connections and the fusible link. I don't like to see 20-30 amps for more than a half minute or so, and 10-15 amps on the ammeter for more than a few minutes doesn't thrill me.
Charging Battery with Alternator - Warning
Wiring is correct voltages at idle is 14.2 volts Rpms at 2000 14.4 steady.
67Dart273
Well-Known Member
The very high voltage means you have something causing the alternator to seriously overcharge what is sometimes called 'full field." Meaning the field is somehow getting full battery current. What I'd do:
Check carefully that the VR is well grounded. Remove it, clean around the firewall bolt holes, the backside and front of the VR around the holes, and remount with star lock washers.
Work the VR connector in/ out several times. Check the wiring, especially the green VR wire that it is not pinched somewhere. If that wire becomes shorted to ground, this problelm will occur
Also Check the alternator brushes that they are NOT grounded to the case. Remove and inspect the alternator brushes. Make sure there is no evidence that the insulators/ mounts are allowing the brushes to ground.
Last, this could STILL be a problem in the supply voltage to the VR. "Up to a point" the lower the supply voltage to the VR, the higher the battery voltage will charge. This, again, is because the VR power/ sensing terminal "thinks" the battery is low and ramps up the field current in an attempt to compensate
See if you can "catch" this problem at home. Monitor battery voltage and bring up RPM to show that it is coming up too much. Then swtich your meter to the ballast power terminal and monitor that. If the ballast is showing "normal" 14V charging voltage, and the battery runs high, the VR has voltage drop between it and the battery, in the harness
Check carefully that the VR is well grounded. Remove it, clean around the firewall bolt holes, the backside and front of the VR around the holes, and remount with star lock washers.
Work the VR connector in/ out several times. Check the wiring, especially the green VR wire that it is not pinched somewhere. If that wire becomes shorted to ground, this problelm will occur
Also Check the alternator brushes that they are NOT grounded to the case. Remove and inspect the alternator brushes. Make sure there is no evidence that the insulators/ mounts are allowing the brushes to ground.
Last, this could STILL be a problem in the supply voltage to the VR. "Up to a point" the lower the supply voltage to the VR, the higher the battery voltage will charge. This, again, is because the VR power/ sensing terminal "thinks" the battery is low and ramps up the field current in an attempt to compensate
See if you can "catch" this problem at home. Monitor battery voltage and bring up RPM to show that it is coming up too much. Then swtich your meter to the ballast power terminal and monitor that. If the ballast is showing "normal" 14V charging voltage, and the battery runs high, the VR has voltage drop between it and the battery, in the harness
.. Thanks sir I'll keep u posted this one is crazy for
Because the radio went out at the same time the alternator went to 18v. I'd say there is a poor connection [that gets worse with heat] and causes low voltage which fools the VR, making it overcharge. Firewall connector and ammeter terminals are the first places I'd look.
I must not be doin it right. I've never heard a VR talk before.
Pawned
N.R.A. Lifetime Member - And damn proud of it
15.4 does not sound outrageous at the alternator. What does the VReg output say.
The voltage will decrease as the battery charges to a full charge
The voltage will decrease as the battery charges to a full charge
Greg hailings
Member
I have a charging issues as well.
Field connector removed from alt shows when tested with key set to Run and using the positive battery terminal .736 volts (again just test wire)
While running the Field shows 13.49 volts
Battery shows 13.53 volts
Alternator is at 15.09 volts
Blue wire at ignition switch connection is showing 14.11
Field connector removed from alt shows when tested with key set to Run and using the positive battery terminal .736 volts (again just test wire)
While running the Field shows 13.49 volts
Battery shows 13.53 volts
Alternator is at 15.09 volts
Blue wire at ignition switch connection is showing 14.11
1. No tricks involved. Set up situation and check the voltages at the connecting locations and current flow to or from the battery.
2. '75 has some wiring differences from earlier models. The changes are not as radical as '76, but the first thing will be to get a '75 FSM and sketch out the charging circuit. You want to be looking at the correct colors and connections!!!
You may notice there were some optional ways to wire the cricuit depending on how the car was equiped.
The next thing to do is a visual check of the lines.
Your looking to see
....if it matches the FSM.
...if there is corrosion, oxidation, broken strands at any of the terminal connections.
...signs of overheating
...chafed worn, cracked insulation on the wire themselves.
Start at the battery positive because that's easy to see. Follow it to the bulkhead connector.
Then go to the alternator's output stud (aka alternator battery terminal). Follow it to the bulkhead connector.
This where you will need the factroy wiring info - the alternator output wire gets a wrapped into a harness with other wires, you can't visually follow it easily if at all.
Then check the regulator and field circuit. It's power comes from the 'ignition 1' or run circuit feed.
Once you know where everything is, at least engine bay side, you can do checks with a voltemeter.
Don't forget to observe the ammeter. Together they will reveal the story.
Welcome to the forum!
Knowing the year and model will be very helpful.
Not all years were wired the same.
Does that make sense to you?
Knowing the year and model will be very helpful.
Not all years were wired the same.
That's odd. With no current flowing, voltage should be either system voltage on the positive side or zero on ground side. Electricity can't flow since the wire is not connected.
That indicates there most of the resistance to flow is between the alternator's output stud and the main splice.
Does that make sense to you?
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