Overcharging alternator and negative ammeter reading

[68charger440]

I have a 68 charger that shows negative on the ammeter.  When I test the voltage on my fluke it shows 18.7 volts.  I changed the charging system to a 1970 and later electronic regulator and dual field alternator setup instead of the old points style regulator setup.  I tried replacing the regulator and had the alternator tested, but it still shows negative on the ammeter and the voltage is still very high.  I replaced some of the wires in the charging wiring harness but not all of them.  Does the gauge of the wiring that I used make much of a difference?  I used some heavier gauge wire than the original.  Could that have reversed the flow of electricity causing the negative ammeter reading etc?
Any ideas?

[Pete in NH]

Hi,


18.7 volts is way too high. I suspect the alternator is running wide open. Unplug the regulator connector and it should drop back to the battery voltage. There should be two wires to the alternator field. One should have 12 volts on it with the key in the run position, the other should go to the voltage regulator. Make sure the one going to the regulator is not grounded along the way. Also, from your description of the negative ammeter reading your alternator output path to the battery sounds like it is open. It could be a blown ammeter or open fusible link.
the fusible link should be a blue colored wire from one of the bulkhead connector pins to the battery terminal on the starter relay. They often have a little rubber/plastic tag on them that says fuse. The gauge of the wiring should not cause this problem.

[b5blue]

Is the battery fully charged?

[Pete in NH]

As I thought about your problem, I was wondering if this is a new conversion to electronic regulation or if the system has been working correctly before this. If it a new conversion, the original 68 alternator has one brush grounded internally and you need an isolated field alternator to make the new electronic regulator work correctly. If you put 12 volts on one field terminal and ground the other, you will see the 18 volts you are getting.

[68charger440]

As I thought about your problem, I was wondering if this is a new conversion to electronic regulation or if the system has been working correctly before this. If it a new conversion, the original 68 alternator has one brush grounded internally and you need an isolated field alternator to make the new electronic regulator work correctly. If you put 12 volts on one field terminal and ground the other, you will see the 18 volts you are getting.

At least part of the problem was existing before the conversion.  After I rebuilt the motor/trans and put it back together I noticed the negative ammeter problem, so rather than just trying to fix the old point style setup I decided to upgrade to newer 70s style setup.  The alternator is a 70s dual field one, with a matching 70s regulator.  The one field wire does have 12v when key is on and when regulator is unplugged the voltage is normal. 

[Cooter]

Make SURE the negative side cable has a damn good ground otherwise the alt. Thinks you always have a stone cold dead battery.

[John_Kunkel]

How does the ammeter read with everything turned off? How does it read with the ignition switch in the RUN position with the engine off?

A short to ground somewhere in the system can cause the ammeter to read discharge while the alternator over-volts to keep up with the discharge.

[68charger440]

How does the ammeter read with everything turned off? How does it read with the ignition switch in the RUN position with the engine off?

A short to ground somewhere in the system can cause the ammeter to read discharge while the alternator over-volts to keep up with the discharge.

It reads ever so slightly to the negative side with key off completely, and with the key in the run position it reads roughly -7 that's my Guesstimate, and that is also roughly where it is when the car is running.  I believe that there is a short to ground somewhere, but I can't find out where and don't know how to find it.  I have pulled all fuses and there is no change so I think it is on a non fused wire somewhere. I can build a motor just fine, but I HATE ELECTRICAL PROBLEMS!!!

[68charger440]

Make SURE the negative side cable has a damn good ground otherwise the alt. Thinks you always have a stone cold dead battery.

It is a brand new battery and I added a new ground wire last week to be sure it was also good.  I put another voltage regulator on it and got it down to 15.8 volts, but that is still too high and it still reads negative on the ammeter.  I still think there is a short somewhere, but where and how do I find it?

[Cooter]

Unless you have some sorta HUGE draw, I'm thinking look at the conn. At the ammeter and at the bulkhead conn.

[Pete in NH]

Is there any chance the ammeter wires were reversed during some dash board work or your rewiring some of the charging circuit? Also, does the electronic regulator have a good ground? Sometimes paint, rust or mounting screws that aren't really tight don't allow the regulator to be really grounded well. Cleaning paint off the firewall mounting point and regulator case and using mounting bolts with internal or external lock washers and real nuts on the bolts help ensure a good ground. Self tapping bolts into rusty kind of stripped out holes don't work so well.

The overvoltage condition and the ammeter reading may be both related to an earlier issue that caused you to convert the system over to the isolated field electronic regulator system or they might be two separate issues. Either way, this circuit isn't too complicated and some troubleshooting should get things working. First, check that the ammeter is wired correctly. Then the regulator ground. With the car not running do you have battery voltage at the alternator output stud? If those things are okay, With the regulator unplugged do you have 12 volts on the blue wire of the regulator connector with the key in the run position. With the car running and the regulator unplugged if you ground the green wire on the regulator connector the alternator output voltage should go way up. Check out those things and let us know what you find. If need be we can go further.

[68charger440]

Is there any chance the ammeter wires were reversed during some dash board work or your rewiring some of the charging circuit? Also, does the electronic regulator have a good ground? Sometimes paint, rust or mounting screws that aren't really tight don't allow the regulator to be really grounded well. Cleaning paint off the firewall mounting point and regulator case and using mounting bolts with internal or external lock washers and real nuts on the bolts help ensure a good ground. Self tapping bolts into rusty kind of stripped out holes don't work so well.

The overvoltage condition and the ammeter reading may be both related to an earlier issue that caused you to convert the system over to the isolated field electronic regulator system or they might be two separate issues. Either way, this circuit isn't too complicated and some troubleshooting should get things working. First, check that the ammeter is wired correctly. Then the regulator ground. With the car not running do you have battery voltage at the alternator output stud? If those things are okay, With the regulator unplugged do you have 12 volts on the blue wire of the regulator connector with the key in the run position. With the car running and the regulator unplugged if you ground the green wire on the regulator connector the alternator output voltage should go way up. Check out those things and let us know what you find. If need be we can go further.

First of all I want to thank all of you for your help.  It gives me the fuel to keep going rather than shooting my car.  Now to answer the questions...
1. I tested the body of the regulator across to a good ground and it tests fine, and just for good measure I connected via alligator clips the VR body to a ground.
2. There is no way I reversed the ammeter wires since I never actually disconnected them when I pulled the cluster out a little to look at it.
3. Here are some test results:
key on regulator connected - blue reg wire 11.9v green 0v red battery wire 12.3
key on reg disconnected - blue reg wire 12.5v green 12.5v red battery wire 12.6
key off reg connected - blue reg wire 0v green 0v red battery wire 12.3
key off reg disconnected - blue reg wire 12.5v green 12.5v red battery wire 12.6
Key on amp draw at battery 4.5  No lights or anything on.  Is this too much of a draw?
key on accessory amp draw at battery .2
key off amp draw at battery 0
The ever so slight negative lean on the ammeter I reported earlier was just the misalignment of the needle since with battery disconnected altogether it still has that ever so slight lean to the left.

[b5blue]

Lets sort out what/how the ALT gauge reads and why.
Firstly with the car off and the battery disconnected where is the needle pointing? Is it dead center on the dial's center mark? No matter if it's off in any direction then any reading you get is offset by that starting point.
The gauge reads the direction of current used by the car so "negative" is from the battery and "positive" is from the alternator. At starting while cranking, your drawing off the battery (Discharging it.) so "IF" the engine starts the first thing your you'll see assuming your charging system is working is a reading in the positive as the battery is fully recharged. The gauge read the draw from the battery and is now reading draw to the battery.
 With the battery fully charged and the charging system working to supply all the cars needs the gauge reads center or very close to center and sits there stable. Now you turn on wipers or any other fairly good draw and what you should see is a reaction bip on the gauge as the gauge "sees" the change in load faster than the regulator corrects output to increase for it, but the needle returns to center and is now steady again. Add another load by turning something else on and the the same thing happens again.
 The ALT gauge reads a comparison of battery VS alt. output. It is not a true AMP gauge as it reads the differential not total output. You could be using 50 amps of alt. output while driving but the gauge will be centered because the battery is full and the car is using/getting what it needs.
 So other readings start to tell you what/where something is wrong but it's not always easy to sort out just what is going on.
Your title "Overcharging alt. and neg. ammeter reading" is confused at best. The gauge can't read on both sides at the same time.    

[68charger440]

Lets sort out what/how the ALT gauge reads and why.
Firstly with the car off and the battery disconnected where is the needle pointing? Is it dead center on the dial's center mark? No matter if it's off in any direction then any reading you get is offset by that starting point.
The gauge reads the direction of current used by the car so "negative" is from the battery and "positive" is from the alternator. At starting while cranking, your drawing off the battery (Discharging it.) so "IF" the engine starts the first thing your you'll see assuming your charging system is working is a reading in the positive as the battery is fully recharged. The gauge read the draw from the battery and is now reading draw to the battery.
 With the battery fully charged and the charging system working to supply all the cars needs the gauge reads center or very close to center and sits there stable. Now you turn on wipers or any other fairly good draw and what you should see is a reaction bip on the gauge as the gauge "sees" the change in load faster than the regulator corrects output to increase for it, but the needle returns to center and is now steady again. Add another load by turning something else on and the the same thing happens again.
 The ALT gauge reads a comparison of battery VS alt. output. It is not a true AMP gauge as it reads the differential not total output. You could be using 50 amps of alt. output while driving but the gauge will be centered because the battery is full and the car is using/getting what it needs.
 So other readings start to tell you what/where something is wrong but it's not always easy to sort out just what is going on.
Your title "Overcharging alt. and neg. ammeter reading" is confused at best. The gauge can't read on both sides at the same time.    

I don't see the confusing part of the title, so let me try to clarify what is going on.  Both statements are true.  The alternator is always putting out it's maximum output at the request of the regulator, and the ammeter is showing a negative draw at all times while running due to a short to ground somewhere. 
The reason both are true is because the short to ground is seen by the regulator as a need to complete the alternator charging circuit, and because the short to ground is always drawing power the ammeter always shows negative while the alternator/regulator combo is always putting out maximum output to try to catch up with the negative draw.  The gauge is not reading both at the same time.  The ammeter gauge is reading negative while my Fluke is reading the constant full output of the alternator/regulator feeding the battery.

[Pete in NH]

Okay, it looks like at first pass the regulator is wired correctly. Lets see if the alternator output stud is connected all the way through to the battery. First disconnect the battery negative cable. Then using your Fluke meter set to a low ohms scale put one probe on the alternator output stud and the other probe on the battery positive terminal/cable. You should see almost zero ohms, anything higher than several ohms and there is something amiss somewhere.

[68charger440]

Okay, it looks like at first pass the regulator is wired correctly. Lets see if the alternator output stud is connected all the way through to the battery. First disconnect the battery negative cable. Then using your Fluke meter set to a low ohms scale put one probe on the alternator output stud and the other probe on the battery positive terminal/cable. You should see almost zero ohms, anything higher than several ohms and there is something amiss somewhere.

It reads 3.26

[HANDM]

I'm gonna throw the    as I am having the exact trouble except upon overcharging for a while, it eats the regulator/ alternator...
I've chased this problem for over three years and still can't get it right...... might be time for a trip to the electrical shop or Craigslist

[68charger440]

I'm gonna throw the    as I am having the exact trouble except upon overcharging for a while, it eats the regulator/ alternator...
I've chased this problem for over three years and still can't get it right...... might be time for a trip to the electrical shop or Craigslist

Mine has also eaten a couple of alternators and regulators, and a Mallory distributor to boot.  If you ever find the problem please post to this thread even if it is years down the road.  I'll do the same.  I'm sure others will appreciate the answer when it is found.

[Pete in NH]

68charger440,

Okay, I think we're on to something.

Here's my theory- If the battery voltage is at 12 volts and the alternator is at 18 volts and you have 3 ohms in between, the difference in voltage is 6 volts. Ohm's law tells us 6 volts divided by 3 ohms is a current of 2 amps. The most you can get through the charging circuit is 2 amps, if the car needs more and even just the ignition circuit needs 4 to 5 amps, it has to come out of the battery so the ammeter swings negative. I think you will find the 3 ohms between the alternator output stud and the one side of the ammeter. The wire from the alternator output stud in the original wiring harness is a black #12 wire that gets to the ammeter through pin P of the bulk head connector. Pin P actually connects to a big wire splice joint and then to the ammeter terminal.You need very close to zero ohms in this path.

So, the next check is to measure the resistance between the alternator output stud to Pin P and then to the ammeter terminal. The possibilities are,the alternator diodes have resistance between them and the output stud, resistance through Pin P ( this is very likely), or something involving the splice joint.

Let us know what you find!   

[68charger440]

68charger440,

Okay, I think we're on to something.

Here's my theory- If the battery voltage is at 12 volts and the alternator is at 18 volts and you have 3 ohms in between, the difference in voltage is 6 volts. Ohm's law tells us 6 volts divided by 3 ohms is a current of 2 amps. The most you can get through the charging circuit is 2 amps, if the car needs more and even just the ignition circuit needs 4 to 5 amps, it has to come out of the battery so the ammeter swings negative. I think you will find the 3 ohms between the alternator output stud and the one side of the ammeter. The wire from the alternator output stud in the original wiring harness is a black #12 wire that gets to the ammeter through pin P of the bulk head connector. Pin P actually connects to a big wire splice joint and then to the ammeter terminal.You need very close to zero ohms in this path.

So, the next check is to measure the resistance between the alternator output stud to Pin P and then to the ammeter terminal. The possibilities are,the alternator diodes have resistance between them and the output stud, resistance through Pin P ( this is very likely), or something involving the splice joint.

Let us know what you find!   

I think you were  onto it...  I got tired of screwing around and replaced both the "P" and the "J" wires bypassing the bulkhead connector altogether both to and from the ammeter.  I also replaced the wire from the alternator output stud to the new wire that I replaced the "P" wire with.  Everything seems to be working correctly now.  The bulkhead connections for both "P" and "J" were pretty burnt up and likely were shorting out there.  Afterward I inspected all of the wires I replaced, and found that at some time in the distant past someone had twisted together a splice on the alternator Battery wire.  I retested it and that wire was where the bad resistance was coming from.  Now I just have to clean up the wires and hope it stays working.  Thanks again to everyone for all of the suggestions and help.

[Pete in NH]

Good to hear you found the problem and have it all working correctly. Wiring around the bulk head connector pins is what the factory did when a 60 amp alternator was installed. Many B body cars were used as police cars and taxis and used 60 amp alternators to power the radios. With the 60 amp alternators the factory wired around the bulk head connector pins and called it the fleet bypass modification. Those connector pins could barely handle the 35 to 45 amp alternators when the cars were brand new. 40 + years later with age and corrosion those bulk head pins are a frequent problem. The fleet bypass mod. is a good one to make on these cars and get those pins out of the circuit.

[HANDM]

68charger440,

Okay, I think we're on to something.

Here's my theory- If the battery voltage is at 12 volts and the alternator is at 18 volts and you have 3 ohms in between, the difference in voltage is 6 volts. Ohm's law tells us 6 volts divided by 3 ohms is a current of 2 amps. The most you can get through the charging circuit is 2 amps, if the car needs more and even just the ignition circuit needs 4 to 5 amps, it has to come out of the battery so the ammeter swings negative. I think you will find the 3 ohms between the alternator output stud and the one side of the ammeter. The wire from the alternator output stud in the original wiring harness is a black #12 wire that gets to the ammeter through pin P of the bulk head connector. Pin P actually connects to a big wire splice joint and then to the ammeter terminal.You need very close to zero ohms in this path.

So, the next check is to measure the resistance between the alternator output stud to Pin P and then to the ammeter terminal. The possibilities are,the alternator diodes have resistance between them and the output stud, resistance through Pin P ( this is very likely), or something involving the splice joint.

Let us know what you find!   

I think you were  onto it...  I got tired of screwing around and replaced both the "P" and the "J" wires bypassing the bulkhead connector altogether both to and from the ammeter.  I also replaced the wire from the alternator output stud to the new wire that I replaced the "P" wire with.  Everything seems to be working correctly now.  The bulkhead connections for both "P" and "J" were pretty burnt up and likely were shorting out there.  Afterward I inspected all of the wires I replaced, and found that at some time in the distant past someone had twisted together a splice on the alternator Battery wire.  I retested it and that wire was where the bad resistance was coming from.  Now I just have to clean up the wires and hope it stays working.  Thanks again to everyone for all of the suggestions and help.

I hope you have found your problem.
As for bypassing the P and J wire, I too have already done that, I think I'll have a look at the harness.......
Mine works for a short time and then back to the same shit....tired of chasing it!

[Pete in NH]

HANDM,

Start a new thread and describe the alternator and regulator on your 69. Is it a single wire regulator and alternator? Pictures of the alternator and regulator help too. This is a simple system and we can take it wire by wire until we find the issue. What is the ammeter showing charging , discharging? What is the battery voltage with the engine running?

[HANDM]

HANDM,

Start a new thread and describe the alternator and regulator on your 69. Is it a single wire regulator and alternator? Pictures of the alternator and regulator help too. This is a simple system and we can take it wire by wire until we find the issue. What is the ammeter showing charging , discharging? What is the battery voltage with the engine running?

There is a thread here some where,
The alternator is a single field green wire type,
I installed electronic ignition
I have no ammeter as it is bypassed
Previously installed a flat regulator as opposed to the black box thinking that was the problem
I just got through repairing the alternator and horn end of the harness as they were somewhat fried
Started the car with the known bad regulator (recently burned out new one) to verify that it isn't charging Reads at 11.7
Plug in known good regulator, alternator immediately starts to overcharge and the rpm's drop. Reads at 17.0 at alternator. yikes!

Thanks, this is really annoying going through regulators and/ or alternators like this.....

[Pete in NH]

Okay,

When you say "flat regulator" do you mean the Chrysler electronic type with a triangle shape, 2 pin,  connector on the front? Also, what type alternator are you using, is it for a 69 with only one field wire connection.

Pictures really help me understand what is on the car. If I could be there in person I could get this thing sorted out very quickly. But, not being able to be there I have to go by your descriptions and I have to ask a lot of questions.

A picture of the regulator and back of the alternator would really help. 

[Dino]

In these situations a faulty alternator or voltage regulator is usually the cause but seeing as this is easily overlooked, make sure your fully charged battery measures around 12.6V between posts and make sure the battery terminal clamps are smothered in dielectric grease and tight.  Also check to see if the battery to engine, and the engine to frame ground straps are in good shape.   

[HANDM]

Yes it is a electronic voltage regulator
Single wire (green) at the alternator
Battery fully charged
All ground connections clean and tight

Checked blue wire (at regulator) key off- 12 volts
Grounded green wire, engine running with no increase in voltage output from alternator

[Pete in NH]

Okay,

I need to know exactly what type of electronic regulator it is. If it is the Chrysler electronic regulator it can not be used with a 69 single field wire alternator.

Again, I really need to know if the regulator is the flat rectangular Chrysler type with a 2 pin, triangle shaped connector on the front or some other type of electronic regulator. There are electronic type aftermarket regulars for 69's available and if that's what you are using I need to know that. That is why I asked for pictures.

If it is the Chrysler type regulator you need to change the alternator to a 1970 and up isolated field type. If you are using a true 1969 alternator you need a different regulator than the 1970 and up Chrysler electronic type.

[HANDM]

Okay,

I need to know exactly what type of electronic regulator it is. If it is the Chrysler electronic regulator it can not be used with a 69 single field wire alternator.

Again, I really need to know if the regulator is the flat rectangular Chrysler type with a 2 pin, triangle shaped connector on the front or some other type of electronic regulator. There are electronic type aftermarket regulars for 69's available and if that's what you are using I need to know that. That is why I asked for pictures.

If it is the Chrysler type regulator you need to change the alternator to a 1970 and up isolated field type. If you are using a true 1969 alternator you need a different regulator than the 1970 and up Chrysler electronic type.

Yes, I am using the electronic two pin triangle regulator bought at oreilly
I have a single green wire on the alternator so yes it is a 69 style alternator

Do I need to install a dual field alternator then? If so where do I run the new field wire to?
Thanks Pete!

[Pete in NH]

Yes, you need to install a newer isolated field alternator to work with that regulator. If you want to keep it looking somewhat like the original 69 alternator, get a 70 or 71 alternator. These were called "round back" alternators and will have two field wire connections.

One field connection will go to 12 volts. There is a blue wire that went to the ING. terminal of the original relay type regulator. This wire should now go to the blue wire on the electronic regulator connector and also continue on to one of the alternator field terminals. The other alternator field terminal should go to the green wire that connects to the green wire on the regulator connector.

You can also use a 1972 on up alternator. these are called "square Back" alternators. The back end looks different than the earlier alternators but, will fit and work fine. The square backs give you a little more output current and the diode assemblies are a little more rugged.

I would also get a new regulator as the old one may have been damaged by using it with the 69 alternator.

I think you should be all set and the long time problem should be solved. Good luck and let us know how it all worked out.

[HANDM]

Thanks Pete

I actually have a spare 72 alternator from a scrapped truck. I'll throw it in after work or this weekend and post back.
All the posts, all the replies and no one but you pointed out that it's the wrong alternator.......thanks again

[HANDM]

Installed the proper alternator and new regulator and it's now charging at 15.0... better than 18.0 but still seems a bit high?
It's an alternator out of a 72 Dodge truck with a 440 that checks out good at oreilly

[Pete in NH]

Hi,

While 15.0 volts may seem a tad high it may really be alright. Keep in mind that most every day voltmeters are at best +or- 2% accurate at best. that's + or- .3 volts so the actual voltage may be some where inside a .6 volt window. Many small meters are more like 3 to 5 % accurate. It's easy to get fooled by a digital meter that gives you an absolute number to forget that number has a calibration tolerance.

Also, these electronic regulators are supposed to be temperature compensated. When cold the voltage is up a bit. When the engine compartment and battery warm up the voltage goes down a bit. If you look in the factory service manual they give you a voltage range based on temperature. At -20F the range is 14.3 to 15.3 volts. 80F is 13.8 to14.4 volts, 140F 13.3 to 14.0 volts and above 140F less than 13.8 volts.

I think you system is working properly but if you still think it is too high you can swap regulators. I've not had good luck with after market regulators over the years and have stayed with Mopar regulators. The current part number is 4529794.

[Skull-1]

Make SURE the negative side cable has a damn good ground otherwise the alt. Thinks you always have a stone cold dead battery.

Can a battery disconnect switch on the negative post screw this up somehow?

Looks like I have a lot of work cut out for me on this thing....

I bet I have the wrong ALT / VR combo....

[Pete in NH]

It could, make sure everything is clean and tight. If you have one of those screw turn knob disconnect switches make sure its tight when the car is running. If the car cranks normally, it is likely okay.

[68charger440]

Just to give an update on the original problem here.  It is close to two months since I started this thread, and my electrical system still seems to be performing correctly.  After 40+ years of wrenching on these cars I will pass on one pearl of wisdom.  Electrical problems are much like cancer, They often spread from one area to another, and you may only be treating a symptom rather than the root cause.  You can make a change that masks the underlying problem for awhile, and then all of a sudden the little SOB rears its ugly head again.  Like with cancer survivors, the rule of thumb is that you don't declare that you are cured, you just count the years that you are cancer free.  After 5 years you can start to talk about being cured.  Sure there are simple electrical problems that are quick and easy fixes, but when you have a 45 year old electrical system with corrosion (cancer), cracked sheathing, and components overtaxed by loads that were beyond those originally spec,d causing intermittent disruptions in current flow, resistance, shorting etc. time is the real test of your repairs.  I have to laugh at those who read a short description of the problem and declare a sure solution.  Its better to point to the possible problems and solutions and let hard work, sound troubleshooting techniques and time prove you right.

[Pete in NH]

Absolutely right! One of the best tools in your tool box for keeping these cars working in the electrical department is a small inexpensive test meter and a plan for how to trouble shoot an electrical system. The meter doesn't have to be anything special a $10 to $20 Radio Shack special will do. Using what it can tell you sure beats guessing and replacing parts.

[68charger440]

Absolutely right! One of the best tools in your tool box for keeping these cars working in the electrical department is a small inexpensive test meter and a plan for how to trouble shoot an electrical system.

... and don't forget the best of all tools for most of us, that mushy mass between your ears!