68 Barracuda Formula S 340 car Charging

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Rustysmopar

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I recently bought is 68 Barracuda 340 formula S car. Some of you may have seen it on craigslist. The car sat in a storage facility for about six years. It’s a solid car and and I got it running after flushing all the fluids.
It seems to be only running on the battery (it cuts off if I unhook the battery while running). I’m not getting 12 V out of the field tab on the alternator, I’m getting 0 and only getting 11.4 on the larger post on the alternator. I’m getting 12.3 volts at the battery. I’ve installed two alternators after I realize the alternator which came on the car was no good. I’ve change the voltage regulator. I’ve replaced the battery, and cleaned every electrical contact and wire point between the alternator and the battery. A couple of questions:

1- could I have gotten 2 bad alternators from Autozone? I will try a third one from them and have them test it before I leave the store with it. The fact that I’m not getting 12 V out of the “field” tab indicates to me that the alternator is no good.

2-I should be getting about 14v at the battery terminals right? That would be the alt charging it.

3- I do not see a ground strap from the block to the frame. Is there supposed to be one and if so where? The negative battery cable is grounded on the block/head and was cleaned and reinstalled.

Thanks folks
Rusty

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Sweet ride Rusty. You probably already know that bad grounds are the bane of most of our electrical problems with these cars. I ran a short ground wire from the back of my alternator, there should be a grounding post, to the block. I also ran a ground wire directly from my negative battery post to the body then to the voltage regulator and to the block to ensure good grounds. These need to have clean metal to give a proper ground. I'm not sure about the old style voltage regulator but the newer style flat regulators must have a good ground from the case to the body. The voltage regulator voltage setting is 14.3 volts. Autozone should be able to test the alternator you have if you think it's suspect. Someone else will jump in to explain much better than I can. Hope this helps some. Good luck.
 
You need a ground strap from the engine to the body. Not really important where it is, a common place is from an empty bolt hole on the back of the head to an existing bolt on the firewall. Make sure it makes good contact to the body, scrape some paint, use star washers.

Do the alternators you are getting have one of the field wires grounded? 69 and back (with the regulator you have) needs one of them grounded.

70 up does not need the ground, has two field wires. They sell the same one for both applications, just the 69 back has the ground.
 
Rustysmopar said:
I recently bought is 68 Barracuda 340 formula S car. Some of you may have seen it on craigslist. The car sat in a storage facility for about six years. It’s a solid car and and I got it running after flushing all the fluids.
It seems to be only running on the battery (it cuts off if I unhook the battery while running). I’m not getting 12 V out of the field tab on the alternator, I’m getting 0 and only getting 11.4 on the larger post on the alternator. I’m getting 12.3 volts at the battery. I’ve installed two alternators after I realize the alternator which came on the car was no good. I’ve change the voltage regulator. I’ve replaced the battery, and cleaned every electrical contact and wire point between the alternator and the battery. A couple of questions:

1- could I have gotten 2 bad alternators from Autozone? I will try a third one from them and have them test it before I leave the store with it. The fact that I’m not getting 12 V out of the “field” tab indicates to me that the alternator is no good.

2-I should be getting about 14v at the battery terminals right? That would be the alt charging it.

3- I do not see a ground strap from the block to the frame. Is there supposed to be one and if so where? The negative battery cable is grounded on the block/head and was cleaned and reinstalled.

Thanks folks
Rusty

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Click to expand...
The charging system is really pretty simple. Like Mike69Cuda said, the alternator on the pre-70 cars only had one field wire, and later had two. If you have a two wire alternator it is for a 70 and up system. The single wire alternators are getting more difficult to find. Can you provide a picture of the back of the alternator you have?
 
67dartgtgo said:
Sweet ride Rusty. You probably already know that bad grounds are the bane of most of our electrical problems with these cars. I ran a short ground wire from the back of my alternator, there should be a grounding post, to the block. I also ran a ground wire directly from my negative battery post to the body then to the voltage regulator and to the block to ensure good grounds. These need to have clean metal to give a proper ground. I'm not sure about the old style voltage regulator but the newer style flat regulators must have a good ground from the case to the body. The voltage regulator voltage setting is 14.3 volts. Autozone should be able to test the alternator you have if you think it's suspect. Someone else will jump in to explain much better than I can. Hope this helps some. Good luck.
Click to expand...



I neglected to state that I grinded paint off the engine bay behind the Voltage Red, the ceramic resistor and the little component next to the battery... is that a solenoid?
I've forgotten more then I remember LOL..

I will ground the block to the frame tomorrow.
 
Ricks70Duster340 said:
The charging system is really pretty simple. Like Mike69Cuda said, the alternator on the pre-70 cars only had one field wire, and later had two. If you have a two wire alternator it is for a 70 and up system. The single wire alternators are getting more difficult to find. Can you provide a picture of the back of the alternator you have?
Click to expand...



Its a two wire..
One larger post and 2 smaller "field tabs".. I actually removed one of the tabs because I thought it may have been touching my valve cover.
 
Ricks70Duster340 said:
The charging system is really pretty simple. Like Mike69Cuda said, the alternator on the pre-70 cars only had one field wire, and later had two. If you have a two wire alternator it is for a 70 and up system. The single wire alternators are getting more difficult to find. Can you provide a picture of the back of the alternator you have?
Click to expand...


Here’s a pic. Any idea where I could find a correct alternator quickly ?

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Bad picture not showing all the terminals. Assuming that you have the original single wire field. You have one smaller wire going to the field (actually a brush), and on the opposite side the brush is grounded to the case (no wire). While running, go to your VR with a jump wire and jump it's two terminals, bypassing it, and forcing maximum output. How much is it charging now?
 
If there is no connection to one field terminal, All you have to do is run a wire from that field connector to ground and it will work fine. It doesn’t matter which one is grounded. The 69 back ones are supposed to have that done.

You can ground it to a bolt on the alternator.

You may also be able to ground it by removing an insulator from the brush holder so the mounting screw grounds it. If you google it you will probably find some images.
 
First, take the current alternator back to Autozone and have them test it. If it works on their tester, the problem probably lies with your car. Second, I would never shop at Autozone. I have heard too much bad about them and their products. I tried them a few times here in Topeka, and was VERY unimpressed. The last time I was there, I tried in VAIN to explain to a clueless girl what I wanted, and wound up walking out.
 
Rustysmopar said:
I’m not getting 12 V out of the field tab on the alternator, I’m getting 0 and only getting 11.4 on the larger post on the alternator. I’m getting 12.3 volts at the battery.
Click to expand...
The Field connection from the regulator will only have system voltage when the regulator is sensing very low voltage.
Steady zero volts when the engine is running shows the regulator is not allowing electricity to the field connection. (how it works shown here in post 5)
Next check is what voltage the regulator is seeing. Do this by measuring voltage at the input connection, labeled 'ignition'. The next nearest location to check with with a probe is the connection at the ballast resistor.

11.4 V on the larger alternator post.
That is the output terminal of the alternator. It should be almost the same voltage as the battery positive terminal under all conditions.
Engine off, lights off, it should exactly the same voltage.

12.3 Volts engine off is a low battery.
11.4 V engine running confirms a batttery with low charge.
Charge that battery with a charger. Do not use the alternator to charge it if at all possible.

Rustysmopar said:
Here’s a pic. Any idea where I could find a correct alternator quickly ?

View attachment 1715729587
Click to expand...

That alternator should work.
If both brushes are insulated and have tab terminals, ground one of them.
Example shown in post 3 of this thread Identifying Chrysler Alternators (1960-1976)

Based on the information so far the most likely issue is no current is flowing into the rotor.
Therefore see if there is voltage on the input side of the regulator with the key in run.
If yes, then check the regulator. Points type regulator is easy to diagnose visually.

After the battery has been recharged using a charger, it would be OK to test the alternator vs regulator using a temporary jumper to power the field.
Do this after the engine is running on slow idle and do not rev the engine.
Because the voltage is not regulated, it will increase with rpm. Any and all electrical devices, including the battery, will draw more current with rising voltage. This can and will cause damage. The ammeter will show how much current the battery is drawing. So that is one way to monitor the danger. If you see the alternator is now working, great. Shut it down and fix the regulator.
 
Last edited:
Mike69cuda said:
You need a ground strap from the engine to the body. Not really important where it is, a common place is from an empty bolt hole on the back of the head to an existing bolt on the firewall. Make sure it makes good contact to the body, scrape some paint, use star washers.

Do the alternators you are getting have one of the field wires grounded? 69 and back (with the regulator you have) needs one of them grounded.

70 up does not need the ground, has two field wires. They sell the same one for both applications, just the 69 back has the ground.
Click to expand...

Hey there and thanks.
The back of the Alts I’m getting has a post with a nut and 2 field tabs. I’m not quite sure I understand your question. If there are two tabs one of them gets grounded and the other one has a plug and which runs back to the firewall and towards the voltage regulator?

If I’m understanding your directions correctly I should run a ground wire from one of the tabs to sheet-metal somewhere?
 
Mattax said:
The Field connection from the regulator will only have system voltage when the regulator is sensing very low voltage.
Steady zero volts when the engine is running shows the regulator is not allowing electricity to the field connection. (how it works shown here in post 5)
Next check is what voltage the regulator is seeing. Do this by measuring voltage at the input connection, labeled 'ignition'. The next nearest location to check with with a probe is the connection at the ballast resistor.

11.4 V on the larger alternator post.
That is the output terminal of the alternator. It should be almost the same voltage as the battery positive terminal under all conditions.
Engine off, lights off, it should exactly the same voltage.

12.3 Volts engine off is a low battery.
11.4 V engine running confirms a batttery with low charge.
Charge that battery with a charger. Do not use the alternator to charge it if at all possible.


Thanks. Great info. I need to ground the block and ground alternator before I do anything else.

I will report back later today or tomorrow. I won’t leave you guys hanging. Lol.



That alternator should work.
If both brushes are insulated and have tab terminals, ground one of them.
Example shown in post 3 of this thread Identifying Chrysler Alternators (1960-1976)

Based on the information so far the most likely issue is no current is flowing into the rotor.
Therefore see if there is voltage on the input side of the regulator with the key in run.
If yes, then check the regulator. Points type regulator is easy to diagnose visually.

After the battery has been recharged using a charger, it would be OK to test the alternator vs regulator using a temporary jumper to power the field.
Do this after the engine is running on slow idle and do not rev the engine.
Because the voltage is not regulated, it will increase with rpm. Any and all electrical devices, including the battery, will draw more current with rising voltage. This can and will cause damage. The ammeter will show how much current the battery is drawing. So that is one way to monitor the danger. If you see the alternator is now working, great. Shut it down and fix the regulator.
Click to expand...
Mattax said:
The Field connection from the regulator will only have system voltage when the regulator is sensing very low voltage.
Steady zero volts when the engine is running shows the regulator is not allowing electricity to the field connection. (how it works shown here in post 5)
Next check is what voltage the regulator is seeing. Do this by measuring voltage at the input connection, labeled 'ignition'. The next nearest location to check with with a probe is the connection at the ballast resistor.

11.4 V on the larger alternator post.
That is the output terminal of the alternator. It should be almost the same voltage as the battery positive terminal under all conditions.
Engine off, lights off, it should exactly the same voltage.

12.3 Volts engine off is a low battery.
11.4 V engine running confirms a batttery with low charge.
Charge that battery with a charger. Do not use the alternator to charge it if at all possible.



That alternator should work.
If both brushes are insulated and have tab terminals, ground one of them.
Example shown in post 3 of this thread Identifying Chrysler Alternators (1960-1976)

Based on the information so far the most likely issue is no current is flowing into the rotor.
Therefore see if there is voltage on the input side of the regulator with the key in run.
If yes, then check the regulator. Points type regulator is easy to diagnose visually.

After the battery has been recharged using a charger, it would be OK to test the alternator vs regulator using a temporary jumper to power the field.
Do this after the engine is running on slow idle and do not rev the engine.
Because the voltage is not regulated, it will increase with rpm. Any and all electrical devices, including the battery, will draw more current with rising voltage. This can and will cause damage. The ammeter will show how much current the battery is drawing. So that is one way to monitor the danger. If you see the alternator is now working, great. Shut it down and fix the regulator.
Click to expand...
 
Rustysmopar said:
Hey there and thanks.
The back of the Alts I’m getting has a post with a nut and 2 field tabs. I’m not quite sure I understand your question. If there are two tabs one of them gets grounded and the other one has a plug and which runs back to the firewall and towards the voltage regulator?

If I’m understanding your directions correctly I should run a ground wire from one of the tabs to sheet-metal somewhere?
Click to expand...

Yep, you can actually just ground one of the tabs to the alternator case easily. As Mattax said, there is a nice picture in post 3 of the modifications. The last picture.
 

Thanks. Great info. I need to ground the block and ground alternator before I do anything else
If the car started, then the block is grounded.
The alternator case is bolted to the head and block makes it the same as the battery ground.
Other items will work better with a the engine to body ground strap, but its not needed for the charging system.
Factory ground for the body is firewall by the heater to the rear of the engine.
 
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