72 Demon Overcharging

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Markzilla88

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Hey guys, I’ve got a 72 Demon with a 360 in it I’m working on. I’ve owned the car for 4 years now and this has never been a problem up until 2 months ago.
I first noticed the battery (duralast) was leaking battery acid out the top ports where you would top the water off, which tipped me off to something new being wrong. When I took it out and cleaned out the engine bay, I started looking for culprits. I found my blue field wire running to the back of the alternator had rattled itself off the field post on the alternator. I’m not sure how long it had been like that, but to that point I had only driven the car twice this year since pulling it out of the garage where I knew everything was correctly in place.
I put the battery on a tender and topped it off (didn’t need much distilled water), I retightened and reconnected the blue field wire to the alternator, and started the car to start measuring voltage to make sure everything was fine. The car now was giving the battery 14 volts at idle and up to 18 volts when throttle was applied.
I have read many threads about what to do, so I cleaned all the connectors in line, cleaned the bulkhead connectors very diligently and put dielectric grease on for good measure. I have cleaned the paint off the casing of the mopar VR and ensured a good solid ground. I also added a grounding wire from the VR to a carb mounting stud. In addition I also added a ground strap from the intake manifold bolt to the brake booster mounting stud on the firewall to help. All of these grounds measured as a good ground on my volt meter.
I then tested the car out to see if this helped or fixed the problem. It has not.
I have tried 4 different voltage regulators and they all produce the same problem. 2 of them are mopar VRs and 2 are Napa parts store VRs.
I checked the alternator as well and it appears to be working as it should. I also put a replacement 60A alternator on there just to check for good measure, and the problem still remains.
Some other tests I’ve run have been put key in the ignition position and tested each field wire while disconnected from the alternator. Battery voltage was 12.4 V with ignition on, Blue field wire reads 11.6V, Green field wire reads .4V.
I also tried briefly disconnecting the field wires from the alternator while car was running. Battery remained at 12.5V. As soon as I reconnected the field wires it went back to charging 14V at idle and up to 18V with any bit of throttle.
With the car running, inside on the dash, the ammeter reads right in the middle at idle, but any throttle causes the ammeter to spike to +40.
It seems like the alternator is doing it’s job charging, but the VR or VR system is leaving the door wide open allowing all the juice the alternator is making to flow to the battery without restriction.
I’m stumped and need any assistance I can get here. Thank you all in advanced.
 
Just had a 71 Duster here with the same problem. It was the blue wire in the harness right before the regulator and the ballast resister. There was a joint there where all the blue wires connect. There was a bad connection. Disconnect the voltage regulator and see if the blue wire has power with the key on. There should be 12 volts at the regulator with the key on. this is what controls the charging .
 
Markzilla88 said:
Hey guys, I’ve got a 72 Demon with a 360 in it I’m working on. I’ve owned the car for 4 years now and this has never been a problem up until 2 months ago.
I first noticed the battery (duralast) was leaking battery acid out the top ports where you would top the water off, which tipped me off to something new being wrong. When I took it out and cleaned out the engine bay, I started looking for culprits. I found my blue field wire running to the back of the alternator had rattled itself off the field post on the alternator. I’m not sure how long it had been like that, but to that point I had only driven the car twice this year since pulling it out of the garage where I knew everything was correctly in place.
I put the battery on a tender and topped it off (didn’t need much distilled water), I retightened and reconnected the blue field wire to the alternator, and started the car to start measuring voltage to make sure everything was fine. The car now was giving the battery 14 volts at idle and up to 18 volts when throttle was applied.
I have read many threads about what to do, so I cleaned all the connectors in line, cleaned the bulkhead connectors very diligently and put dielectric grease on for good measure. I have cleaned the paint off the casing of the mopar VR and ensured a good solid ground. I also added a grounding wire from the VR to a carb mounting stud. In addition I also added a ground strap from the intake manifold bolt to the brake booster mounting stud on the firewall to help. All of these grounds measured as a good ground on my volt meter.
I then tested the car out to see if this helped or fixed the problem. It has not.
I have tried 4 different voltage regulators and they all produce the same problem. 2 of them are mopar VRs and 2 are Napa parts store VRs.
I checked the alternator as well and it appears to be working as it should. I also put a replacement 60A alternator on there just to check for good measure, and the problem still remains.
Some other tests I’ve run have been put key in the ignition position and tested each field wire while disconnected from the alternator. Battery voltage was 12.4 V with ignition on, Blue field wire reads 11.6V, Green field wire reads .4V.
I also tried briefly disconnecting the field wires from the alternator while car was running. Battery remained at 12.5V. As soon as I reconnected the field wires it went back to charging 14V at idle and up to 18V with any bit of throttle.
With the car running, inside on the dash, the ammeter reads right in the middle at idle, but any throttle causes the ammeter to spike to +40.
It seems like the alternator is doing it’s job charging, but the VR or VR system is leaving the door wide open allowing all the juice the alternator is making to flow to the battery without restriction.
I’m stumped and need any assistance I can get here. Thank you all in advanced.
Click to expand...
Have you had the battery checked? Any Car parts store should be able to do it for you.

It has to be a load test, not just a voltmeter check.
 
I've written "books" on this but the problem is SIMPLE. The VR MUST BE at battery voltage PERIOD. This means ZERO voltage drop from BATTERY to VR in both the ground path and the positive/ harness

"How do you tell?" Easy

1..Turn key to "run" with engine stopped. Get a multimeter as close to the VR as you can with ALL wiring connected normally. With no work, you can back-probe the blue wire at the alternator field, or the high side of the ballast. As Steve, OldManMopar mentioned, this comes from the same place--the dark blue "run" line coming through the firewall.

Now stab your remaining probe directly into the battery POS post. Whatever you read is the voltage drop. You want this reading the lower the better, zero would be perfect. Anything more than say 3/10 of one volt you need to investigate

2...Ground. Run engine to normalize battery, and make this test first with no accessories powered, and again with all you can find to power on, lights, stereo, heater, etc. Run engine at simulated "low to medium" cruise AKA the fast idle cam.

Stab one probe hard into the mounting flange of the VR and the other into the top of the NEG battery post. Reading should be VERY low, zero is perfect
===================================


CAUSE OF DROP. The dark blue feeding the VR starts clear back at the battery. BATTERY----FUSE LINK---THROUGH FIREWALL CONNECTOR---to AMMETER--through AMMETER--out AMMETER on LARGE BLACK and to LARGE WELDED SPLICE this is in harness, a few inches from ammeter, behind cluster---BRANCH OFF to fuse panel, headlights AND TO IGNITION SWITCH CONNECTOR---THROUGH SWITCH and back out IGNITION SWITCH CONNECTOR--to and THROUGH FIREWALL CONNECTOR on dark blue, into engine bay and BRANCH OFF to feed ignition, VR, alternator field, electric choke, idle stop if used, smog devices if used.

All the CAPITAL items are of particular interest. A few hundreds drop here, an few tenths there.

On my 67 Dart, it was MORE than 1 1/2 volts drop!!!

==================================

HOW TO FIX

Consider bypassing the ammeter and that entire circuit can be part of the problem

Without doing a bunch of mods, one way is to add a relay. Electrically cut the dark blue "ignition run" line coming into the engine bay. Use the firewall end of the wire to trigger a Bosch style relay. Feed the contacts of the relay from the big stud on the start relay with a fuse/ breaker, use say no12 wire.

Connect the engine bay cut end of the wire to the switched contact of the VR, and if you STILL have problems double check for V drop

==================================

AND ALSO SUSPECT THE VR CONNECTOR ITSELF

It is difficult to check these, but you can buy replacement pigtails various places, and you an "work" the connector in/ out several times to scrub the terminals. Inspect the terminals for corrosion, and as you work the connector, "feel" for tightness. Also a .177 caliber gun cleaning brush can be used to clean those female terminals, as well as the flat trailer light connectors, AND the 2 wire distributor pickup connectors.

(On my long ago gone, beat up, Mopar swapped FJ-40 Landcruiser, I actually SOLDERED the wires to the VR after gutting the connector and pushing it on as a "dummy." I do not recommend that for obvious inconvenience issues.)
 
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ARE MOPARS WORSE than "everybody else?"

Maybe............WHY?

Mopar VR sensing is on the VR POWER wire, and as I outlined, that "ignition run" line is SHARED by other circuits. Voltage drop is the issue.

Simple. Ford/ GM all use regulators with a separate, dedicated, voltage sense wire. THIS WIRE has NO current from other uses. Since it is only for sensing, there is VERY LITTLE current drawn in that wire. It is a DIRECT path from the VR to the battery.

Now Ford/GM CAN suffer over-voltage due to grounding problems, but the issue of harness drop is largely eliminated
 
Connections I have found to be in poor condition is in the Alternator's output circuit. Wire R6 on the factory diagrams.
This will not show up in the test for voltage drop from the battery (engine not running).
It will only show up by testing with the alternator providing power.
Testing is basically the same as described by @67Dart273 but the reference point is the alternator's output stud (marked Bat) and the alternator must be producing power at high voltage than the battery.

In a car with standard wiring, there are either 2 or three connections in this wire.
Either:
One at the alternator and at the firewall.
or some time after 1970
One at the alternator, an engine connector, and at the firewall.

(1960-61?, 1975 and 1976 are a little different in connections but same concept.)

Example of heat damaged alternator output wire terminal removed from the bulkhead connector.
1691339902534.png


This was cause by driving after jump starting a very drained battery.
Damaged wire crimp from this time onward has more resistance than when it was in good condition.
Oxidation of the terminals adds resistance too. The foam seals were long past their service life. This is a Year One / MH harness so these issues can occur even if the harness has been replaced or repaired.

Oxidation is another caused
 
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^^Just to make it clear,...................That voltage drop, while a waste of power and can cause wire / terminal heating, IS NOT the cause of overcharging.
 
Causes of overcharge:

1...VR IS NOT at exactly the same as battery voltage
2...VR has an internal problem, AKA temp compensation, circuitry is out of tolerance
2....Rare, but sometimes battery problems, such as sulfation.
 
67Dart273 said:
^^Just to make it clear,...................That voltage drop, while a waste of power and can cause wire / terminal heating, IS NOT the cause of overcharging.
Click to expand...
??

If you mean charging a dead battery then yes .
But resistance in the alternator outpout wire surely can cause overcharging. No ?

Lets say the car has just been started and the battery is charging.
Power flows from the alternator through the damaged bulkhead connection and loses voltage right there, before it even gets to the main splice.
 
You know I like pictures.

Same example with resistance only at the output wire's bulkhead connection.
1691340798049.png


As you've pointed out many times, resistance can cause voltage drop even if it's too small for a typical multimeter to measure.
V=I x R
In this example, if I did the math right
1.5 Volts = 25 amps x Resistance
.06 Ohms = Resistance.
 
Mattax said:
??

If you mean charging a dead battery then yes .
But resistance in the alternator outpout wire surely can cause overcharging. No ?

Lets say the car has just been started and the battery is charging.
Power flows from the alternator through the damaged bulkhead connection and loses voltage right there, before it even gets to the main splice.
Click to expand...
No. In Mopars the sense comes FROM THE splice at the ammeter, so the ignition circuit is seeing the first common load point from the alternator, or to put it another way, the welded splice is the common point.

If there is resistance in the output, all that happens is,............the output heats up and wastes power. But the sense to the VR says, "oh, the battery is low," we don't know why, but let's ramp up field current to compensate. So the VR ramps up field, the alternator puts out more, the resistance in the output wire heats up the circuit, but the output at the battery remains the same, because the sense circuit of the VR is now satisfied.

In a manner of speaking the same thing is happening in overcharge. If there is resistance/ voltage drop in the SENSE circuit, ALL THE VR SEES is that the sense voltage to the VR is LOW, so the VR ramps up field, the alternator puts out more, the sense V eventually comes up to satisfy the VR setpoint. NOW the difference is, the resistance is in the sense line, which is ESSENTIALLY THE PATH from BATTERY TO VR. So now since the VR is satisfied AT THE SENSE TERMINAL, the VR knows not what is actually happening AT THE BATTERY
 
67Dart273 said:
I've written "books" on this but the problem is SIMPLE. The VR MUST BE at battery voltage PERIOD. This means ZERO voltage drop from BATTERY to VR in both the ground path and the positive/ harness
Click to expand...
100 percent accurate. Any voltage loss from batt value, will overcharge batt.
 
Mattax said:
You know I like pictures.

Same example with resistance only at the output wire's bulkhead connection.
View attachment 1716123813

As you've pointed out many times, resistance can cause voltage drop even if it's too small for a typical multimeter to measure.
V=I x R
In this example, if I did the math right
1.5 Volts = 25 amps x Resistance
.06 Ohms = Resistance.
Click to expand...
The resistance has to be in a place that only affects the VR as opposed to the output path to the battery. From alternator, bulkhead, splice, bulkhead, back to battery there is no place there that can affect the VR without also affecting the load. Now if the ignition switch feed is resistive, YES that can cause a problem or if there is drop in the switch (on the road to the VR) that also.

All of what you have there along the bottom, from the alternator to the battery, can not normally cause the VR to see low. So you are kinda right in that "some parts" may cause a problem, but that is why you check all the way from the battery to the VR.
Of course ACTUALLY checking right at the VR is better, but you would have to backprobe the VR connector with a pin probe, etc
 
OK I see what you are saying, and how its different than what I'm looking at.
I agree the battery will not get overcharged with resistance in the alternator output wiring.
And the battery will see higher voltage if there is resistance in the sense line going ignition switch and wiring to the regulator.
 
Since I was doing pictures, here's how it looks with the biggest voltage drop between the main splice and the regulator.
1691342554272.png


The resistance could be in the column connections (either one or both), the ignition switch, or the bulkhead run wire. Or all of them. But the end result is the regulator is allowing enough field current so it senses 14 Volts even this causes the battery to actually be getting power over 15 Volts. That causes the battery to overcharge.
 
67Dart273 said:
The resistance has to be in a place that only affects the VR as opposed to the output path to the battery. From alternator, bulkhead, splice, bulkhead, back to battery there is no place there that can affect the VR without also affecting the load. Now if the ignition switch feed is resistive, YES that can cause a problem or if there is drop in the switch (on the road to the VR) that also.

All of what you have there along the bottom, from the alternator to the battery, can not normally cause the VR to see low. So you are kinda right in that "some parts" may cause a problem, but that is why you check all the way from the battery to the VR.
Of course ACTUALLY checking right at the VR is better, but you would have to backprobe the VR connector with a pin probe, etc
Click to expand...

I know this thread is a bit old but figured it was better to respond here than start a new one. I have a slight overcharging issue in my '70 Duster, where should I put the voltmeter leads when probing the voltage regulator and what should I be reading to determine if the problem is the regulator or elsewhere? A while back (~5 years) I did the mod where I added a relay between the ignition switch and regulator because it was sensing a false low voltage and that fixed it but today I noticed my volts gauge in the car was reading over 15 and I confirmed with a good multimeter it's charging at 15.3V. Battery is good btw, voltage with the car off is 12.5+ at the terminals.

EDIT: Also if it's relevant the ammeter is gone, basically redid that whole circuit and bypassed the bulkhead connector then added a volts gauge.
 
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See post #5.

Excellent diagnostic procedure by 67 Dart273.
 
Just performed the checks, looks like the regulator is bad. Saw a max voltage of 0.4-0.5 between the body of the regulator and battery negative post with the headlights on and blower motor running, with those things off it was less than 0.1V. It did last 5+ years but when I pulled the VR off to make sure it had a clean ground to the firewall I saw "Made in China" on the back... this time I'll spend a little extra on an ACDelco unit (made in USA) from O'Reillys.
 
67Dart273 your a badass!! You really know your ****!! Thanks for valuable info...makes sense...., Will
 
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