Low charge on 68 Cuda

-
mrose

mrose

Active Member
Joined
May 2, 2015
Messages
35
Reaction score
1
Location
Pennsylvania
I need some help figuring out why I can't get a good charge going. Here's the set up:
68 cuda with a 69- 340 in her. Just totally redone. all new wiring harness's from year one. The alternator is new and when checked on a store machine tests good and at 14.5 volts out, it is a double field alt and I am only hooking up to the one "field" lead that fits the stock wiring connecter, this is what the manufacturer of the alt advised me to do and I even tried jumping the two which is another thing they had me try. The battery is good and I just replaced the VR. I have checked all the grounds and even double grounded the Alt and VR with separate grounds. Everything else electrically works on the car but the voltage at the alt and battery is around 12.1 and on a bat/charging system tester doesn't even get to the "charging area" on the machine. The gauge in the car does move back and forth as you increase the RPM's and put a load on it but as in the past before the rebuild if I drive it at night it is going to kill the battery and leave me stranded. Much of the reason I did the rebuild was to correct this issue and it seems it hasn't. The only thing really left in the "old" system is the original ignition key unit and the headlight switch which I can't see would have anything to do with this issue.
Please let me know if you need any additional information to make a diagnosis.
Many Thanks
 
First double field is not quite true, it has one field but both connection are on terminals. In the early alternators one connection was internally connected to ground. If you are using an early regulator, take that spare field connection and ground it. Early regulators placed 12V using a relay in a normally closed fashion to energize the field. As the voltage reached the desired limit the relay coil opened contacts, cutting field, it was an on going chattering. There are electronic ones now for replacement, for early use.

When the electronic regulators came out, the alternator was changed so the grounded connection was brought out isolated instead. The new regulators, sinks current to ground, the other alternator lead receives 12V when key is on. I can go on and say why this is all better, but most do not care, and arc and spark wires to try to fix.
 
Hey Kit, Thanks for the reply. The alt has a wider blade "field" connector and a smaller blade connector. The stock wire connector fits the thinner blade. I have tried a different combination of switching those around and also using a jumper to ground them with no avail?
Does it matter which field terminal on the alt the stock wire is connected to?
 
mrose said:
Hey Kit, Thanks for the reply. The alt has a wider blade "field" connector and a smaller blade connector. The stock wire connector fits the thinner blade. I have tried a different combination of switching those around and also using a jumper to ground them with no avail?
Does it matter which field terminal on the alt the stock wire is connected to?
Click to expand...

It should not matter. I would test connections first at alternator to check if they are isolated from body, they should be. There should also be continuity of a few Ohms, at the terminals. A test at idle one lead 12V, the other ground, will provide full field for alternator test. Voltage can be high, do not rev engine, keep test short.

The polarity of the connections does not matter, because the field winding, on the rotor core magnetizes convoluted end plates. The end plates are interlaced so the field is N-S-N-S..... with rotation, and even rotation direction, does not matter.
 
WHAT REGULATOR are you using?

If you are using the 69/ earlier style regulator for the older grounded field (original) then hook your field wire to one field terminal and ground the remaining terminal.

On some alternators you can ground that field by removing insulating washers from the brush mount. IF YOU DO that cut off the spade so that a field wire cannot accidently be connected
 
67Dart273 said:
WHAT REGULATOR are you using?

If you are using the 69/ earlier style regulator for the older grounded field (original) then hook your field wire to one field terminal and ground the remaining terminal.

On some alternators you can ground that field by removing insulating washers from the brush mount. IF YOU DO that cut off the spade so that a field wire cannot accidently be connected
Click to expand...

I am using the old style, see attached photo's it was for 1969 & older.
Kit, I also checked continuity with the 2 Field terminals and the body and there is no continuity. There is .01 ohms when touching the 2 field terminals.
And for the test you want me to take one lead of my tester to the screw terminal and one lead to a body/engine ground, correct? And do I disconnect the current wiring harness leads to the alternator for this test?
Start the car and see what voltage I get? is that correct?

IMG_0849.JPG


IMG_0845.JPG


IMG_0846.JPG
 
As I said you need to ground the field terminal not connected to the field
 
What is being said sounds like some confusion may be going on. You are not being told to connect your 'tester' anywhere; you are being told how to connect the 2 fields terminal on the back of the alternator.

One connects to the green wire coming from the regulator and which connects to the FLD terminal on the regulator. Both ends of that green wire look correctly connected. The other field terminal on the back of the alternator should connect to a nearby ground, which is missing in the 3rd pix. Also, make sure there is a ground jumper from the back of the passenger side head to the firewall. And sometimes a ground wire from the ground terminal on the older style regulator ( that screw on the side) to a clean metal connection on the firewall will be needed.

With this, the system should operate and charge, and you should read around 13.5 to 14 volts typically across the battery terminals with a voltmeter, at idle after it has run a minute or 2. It might vary a bit at first depending on the state of the battery's charge.

If you don't see this, then, while running:
- Check to see if you have around 12 volts at the blue lead going into the regulator
- Check the voltage at the green FLD wire at the regulator, it should typically be in the 2-3 volt range.
 
nm9stheham said:
What is being said sounds like some confusion may be going on. You are not being told to connect your 'tester' anywhere; you are being told how to connect the 2 fields terminal on the back of the alternator.

One connects to the green wire coming from the regulator and which connects to the FLD terminal on the regulator. Both ends of that green wire look correctly connected. The other field terminal on the back of the alternator should connect to a nearby ground, which is missing in the 3rd pix. Also, make sure there is a ground jumper from the back of the passenger side head to the firewall. And sometimes a ground wire from the ground terminal on the older style regulator ( that screw on the side) to a clean metal connection on the firewall will be needed.

With this, the system should operate and charge, and you should read around 13.5 to 14 volts typically across the battery terminals with a voltmeter, at idle after it has run a minute or 2. It might vary a bit at first depending on the state of the battery's charge.

If you don't see this, then, while running:
- Check to see if you have around 12 volts at the blue lead going into the regulator
- Check the voltage at the green FLD wire at the regulator, it should typically be in the 2-3 volt range.
Click to expand...


Thank you for the feedback, I will try this and report back. Blessings
 
OK Guy's, I have tried all you have suggested with the same results, It is still not charging only reading 12.1 volts at the battery when running on a tester, will not get in the charging range, which is 13.8 to 14.5 on the charging system tester. The tester is new and I checked it on another car to make sure it wasn't the tester. I have tried switching around the two field leads on the back of the alternator back and forth to see if that makes a difference and it doesn't.
Not sure what to try next............
 
mrose said:
OK Guy's, I have tried all you have suggested with the same results, It is still not charging only reading 12.1 volts at the battery when running on a tester, will not get in the charging range, which is 13.8 to 14.5 on the charging system tester. The tester is new and I checked it on another car to make sure it wasn't the tester. I have tried switching around the two field leads on the back of the alternator back and forth to see if that makes a difference and it doesn't.
Not sure what to try next............
Click to expand...
I am going now to read voltage at VR blue and green wires and will post that in a couple minutes.
 
mrose said:
I am going now to read voltage at VR blue and green wires and will post that in a couple minutes.
Click to expand...
Ok Guys here's what it is reading at the VR....Going to the blue lead at the VR-11.91V and at the green - 4.67V
Let me know what you think.
 
What is the voltage at the output stud of alternator? I would expect the VR green terminal to be higher than 4.67V, because the field should be near full on, based on the low blue terminal voltage.
 
Last edited:
Since you already have the isolated field alternator,
IMO;the best upgrade would be to install the matching regulator. With that done, you can look forward to nearly decades of a trouble-free charging system.
It's so easy to do.
 
Sounds like the VR you have is either bad or NOT GROUNDED but you are on the right track.
 
AJ/FormS said:
Since you already have the isolated field alternator,
IMO;the best upgrade would be to install the matching regulator. With that done, you can look forward to nearly decades of a trouble-free charging system.
It's so easy to do.
Click to expand...

If the OPs VR turns out to be bad, you can do this, add one more wire for the new alternator field.
 
KitCarlson said:
What is the voltage at the output stud of alternator? I would expect the VR green terminal to be higher than 4.67V, because the field should be near full on, based on the low blue terminal voltage.
Click to expand...
voltage at the stud of the alternator is 12.1
 
AJ/FormS said:
Since you already have the isolated field alternator,
IMO;the best upgrade would be to install the matching regulator. With that done, you can look forward to nearly decades of a trouble-free charging system.
It's so easy to do.
Click to expand...
Not sure I get this AJ
 
67Dart273 said:
Sounds like the VR you have is either bad or NOT GROUNDED but you are on the right track.
Click to expand...

VR is brand new and It is grounded to the firewall and I actually used a jumper and ran a ground from the screw on the case to the Neg battery ground on the block?
 
"New" does not mean functional." You may have been unlucky and gotten a defective VR, or inadvertently ruined the one you have

The 69/ earlier system (that is your VR) runs power TO the field, through the field and to ground.


Therefore to see if the alternator charges, disconnect the VR and jumper the two wires together, this will feed full 12V (full field) to the alternator. This should cause full output. Don't rev the engine, and don't allow the voltage to climb above 15.5--16V. Control with throttle.

The 70/ later system, the VR "controls the ground" on the field. On those, the field gets power (blue) from the ignition feed, and returns to the VR which grounds / ungrounds the field to control it. Adding one more wire is all you need to run the new regulator

A quick look at the simplified diagram ........Everybody likes to call these "dual field." THIS IS INCORRECT. The correct term is "isolated field"

Dual_Field_Alternator_Wiring.jpg


Conversion and differences:

MyMopar - Mopar Forums & Information - Mopar Charging System Overview and Conversion

69 / earlier, one field brush is GROUNDED

pic1.gif


70 and later.........

pic2.gif



You can download free manuals at MyMopar........

MyMopar - Mopar Forums & Information - MyMopar Tools/Reference
 
Well, there is the early electro-mechanical type VR like you have with just the one green wire going to the alt; and the second post of your LATE style sq. back alt. to be grounded to the battery. Being the device it is, it has a tendency to "act up,or act funny", and has a higher failure rate, than the Solid state later VR.
The later VR, with two wires going to the alt, one to each of those field connections,Is very nearly trouble free;so long as it remains well-grounded.
There is also a Constant Voltage VR available, which I have been using on my Optima since about 2004.That system has been trouble free, except for requiring the occasional brush replacement.The alt is circa the early 70's. The trunk mounted Optima is circa 2000
 
So what happens when you remove the blue and green wires from regulator and connect them together ? That would give full field, to test alternator, the alternator post voltage should increase. Do not rev engine, the voltage and current may go too high. Your battery is very low on charge, the voltage may take a few minutes to increase.
 
Last edited:
You must log in or register to reply here.
-

Back
Top