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Battery Voltage reading extremely high!

Rusty 72

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Hi all.
So I have a 1972 Charger that when purchased it had an entirely burned wiring harness due to the Alt. From what I've read its a common issue...sadly. Anyway, I removed the entire interior and engine harness and installed a MSD box and single wire Alt, pretty much hot wiring it so I could move it around until I could source another harness.
Ive recently acquired a new (used) harness for the interior and engine. I followed the Mad Electrical instructions on by passing the Alt and adding a few fusible links and installed everything. I kept the MSD box and single wire Alt installed.
Now its running fine and I have all electrical again but when I checked the battery when it was running it read 38-40 volts! I quickly shut it down and rechecked the battery with it off and off it read 12.4. Started it up again and the same thing 38-40 volts. So I shut it down.
The Alt was working fine previous to me installing the new harness?? I cant figure out what would be causing it? The Mad Electrical diagram has the power going from the starter relay battery post thru the system and back to the relay post. I thought this odd? could that be causing the issue? or maybe I don't have a ground connected correctly on the interior?
Sorry for the long post.
Thanks in advance Jeanette
 
It'll be interesting what others think but in the meantime I'd check the voltage regulator. I remember getting my alternator bench tested once and the tech said something about they can overcharge if the voltage regulator isn't working. Also, check to make sure the voltage regulator has a good ground.
 
It'll be interesting what others think but in the meantime I'd check the voltage regulator. I remember getting my alternator bench tested once and the tech said something about they can overcharge if the voltage regulator isn't working. Also, check to make sure the voltage regulator has a good ground.

If he’s running a one wire alternator he dosent have a regulator.

But I’ve never seen one that high.

Unless maybe the alternator shorted and is going full field?

I’d start by getting the alternator tested to eliminate that as a variable. JMHO.
 
Check your voltmeter, never heard/seen such a thing!
 
I has to be a connection some where as the amperage needed to get to 40 volts would be high
bad reg or it is not seeing the voltage and is trying to over come
 
All good tips! That voltage is extremely high. Start with the easiest as suggested above, the battery in your volt meter as well as the meter.
Are you using a 2 pole alternator as a single, if so one of the poles has to be grounded to the case. Make sure the voltage regulator is grounded as well.
 
A2C03A37-F0C9-472A-AAF5-7513744D035A.jpeg
812BA54C-A28B-4AFD-B33B-73E30638E28F.jpeg
2 wire on top and 1 wire on the bottom
If he’s running a one wire alternator he dosent have a regulator.

But I’ve never seen one that high.

Unless maybe the alternator shorted and is going full field?

I’d start by getting the alternator tested to eliminate that as a variable. JMHO.
Didn’t want to give ya a red x but there is a voltage regulator for a 1 wire as well as a 2 wire. I do agree with the rest of the statement on getting the alternator bench tested to eliminate that as a variable.
 
Thanks for all the responses.
It’s a single wire alt with an internal regulator. Just ground the case and a single wire to either the positive battery post or the battery post in the starter relay.
I will check my handheld cheap volt meter. Maybe it’s bad. I will also pull the alt and have it tested.
Thanks Jeanette
 
Ok hold on. I’m just reading this again. So I need to use and additional regulator with this one wire alt?
 
Ok hold on. I’m just reading this again. So I need to use and additional regulator with this one wire alt?
No... And for the Nay Sayers an Alternator will push the voltage well past 100 volts if full fielded.... In the 80's & 90's that's exactly what the manufacturers were doing to run those heated/de-ice windshields... But they would isolate the alternator from the chassis when the windshield circuit was energized... To prevent blowing stuff up... Like batteries, radios, bulbs & modules....
 
For the alternator to push the voltage that high it is full fielded, which means the regulator is either failed in the charge mode or it's bypassed... The problem is in the alternator...
 
Are you running a single wire delco?...what ever a alt it is... take the alternator off and have a a parts shop bench test it. It won`t take long and they should do it for free, and if it is putting more volts then what its suppose to you'll know. You can weld with 24v...48V hard to even imagine.
 
What is the alternator? Is it an aftermarket alternator, or an older Mopar single wire? Mopar alternators have internal rectifiers, but not regulators.
 
It’s a single wire tuff stuff I got within the last 5 yrs. I had used it on another project until I swapped it into the Charger.
I’ll pull it and have it checked.
Thanks again!
 
What is the alternator? Is it an aftermarket alternator, or an older Mopar single wire? Mopar alternators have internal rectifiers, but not regulators.

They piggy back one of these on the alternator...
Screen Shot 2019-07-22 at 21.09.57.png
 
What is the alternator? Is it an aftermarket alternator, or an older Mopar single wire? Mopar alternators have internal rectifiers, but not regulators.

Think you are mistaken, Mopar uses a voltage regulator.
 
To original poster, can't imagine how an alternator could produce 38-40 volts. Check the range setting on the volt meter. 12.4 is normal, 14.5 or so with good alt running.
Make sure the voltage regulator has good ground, my experience is bad ground gives no alt output. What sort of "1 wire" alt do you have?
 
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If the regulator circuit can't detect battery voltage the field current will be commanded to full output. Is the alternator case /engine block grounded correctly? If so the problem lies internally in the alternator.
Doug
 
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