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Overcharging on 70 challenger FIXED #2744667
02/19/20 05:16 PM
02/19/20 05:16 PM
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Abilene, Texas
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Can some one tell me what is supposed to happen when you unplugging the voltage regulator from the wiring harness? Does it charge more or less than it should. Friend is having trouble overcharging and I’m trying to diagnose it over the phone.

Last edited by fastmark; 02/27/20 09:07 AM.
Re: Overcharging on 70 challenger [Re: fastmark] #2744724
02/19/20 08:26 PM
02/19/20 08:26 PM
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Lincoln Nebraska
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unplugging the reg should elim all charging. OE electromechanical reg? EDIT I'm thinking (likely) reg or alt internal issue

Last edited by RapidRobert; 02/19/20 08:33 PM.

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Re: Overcharging on 70 challenger [Re: RapidRobert] #2744745
02/19/20 09:06 PM
02/19/20 09:06 PM
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Originally Posted by RapidRobert
unplugging the reg should elim all charging. OE electromechanical reg? EDIT I'm thinking (likely) reg or alt internal issue


70 would be electronic.

How much is it overcharging ? Any current or voltage measurements ?? He's going to have to get familiar with a voltmeter and start with some readings. Might get lucky with throwing parts at it or maybe not twocents beer

Re: Overcharging on 70 challenger [Re: TJP] #2744753
02/19/20 09:22 PM
02/19/20 09:22 PM
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Abilene, Texas
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It pegged the ammeter one day and he found a loose ground. He thought that fixed it. He had the alt checked and regulator checked and both were good? It still puts out 16 V. I don’t have a space in my shop to look at it right now. I’m thinking the regulator is bad or it has a shorted wire. It all new M&H wiring and worked for 1000 miles after I installed it.

Re: Overcharging on 70 challenger [Re: TJP] #2744754
02/19/20 09:24 PM
02/19/20 09:24 PM
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If it is an electronic regulator have him make sure it's not rusty or freshly painted under the mounting points. I found out the hard way those regulators have to be grounded good.


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Re: Overcharging on 70 challenger [Re: slantzilla] #2744756
02/19/20 09:25 PM
02/19/20 09:25 PM
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Originally Posted by slantzilla
If it is an electronic regulator have him make sure it's not rusty or freshly painted under the mounting points. I found out the hard way those regulators have to be grounded good.


Already done that.

Re: Overcharging on 70 challenger [Re: fastmark] #2744764
02/19/20 09:39 PM
02/19/20 09:39 PM
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When it is acting up unplug the regulator. If it quits charging could be the regulator. I have seen two things happen at the alternator. One the regulated to ground brush terminal or insulators failed and grounded to the case causing full fielding and two shorted to ground armature or slip rings again causing full fielding and overcharging. Even though the harness is new if the regulator 12 volt feed connection is poor or bad the regulator looses voltage sense and reacts by trying to charge what it thinks is a low or dead battery.

Last edited by NITROUSN; 02/19/20 09:40 PM.
Re: Overcharging on 70 challenger [Re: NITROUSN] #2744956
02/20/20 02:52 PM
02/20/20 02:52 PM
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Rio Linda, CA
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Also, check the green wire from the alternator where it's routed over the valve cover; a short to ground here will cause full fielding.


I'm supposed to respect my elders, but its getting harder and harder for me to find one now.
Re: Overcharging on 70 challenger [Re: fastmark] #2745037
02/20/20 08:06 PM
02/20/20 08:06 PM
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Phila. Pa.
Mattax Offline
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Originally Posted by fastmark
It pegged the ammeter one day and he found a loose ground. He thought that fixed it.

On the face of it, this doesn't add up.
I can't think of a poor or missing ground that would cause the battery to discharge or for it to recharge like crazy.
Two suggestions on this:
1. Ask which way the ammeter pegged. Charge or discharge ?
2. Often the alternator output wires are confused for grounds because they are black insulated. Chrysler used black and red inuslation for positive feeds. Think of it like house wiring - black and red are both hot. Unlike house wiring, black is also used on grounds.

My guess is that there is a poor connection(s) on the alternator output and most likely a poor connection(s) from the alternator output to the voltage regulator.

To check that, measure the voltage between the alternator output post and the nearest exposed junctions to the voltage regulator's sensing terminal.
That will probably be the field terminal with the blue wire. Another one will be the ignition wire (blue) at the ballast resistor.
If its 1 Volt or over, while the alternator is running, and nothing else on then the VR is doing its job, but its getting faulty information.
Look at the ammeter to see if the battery is charging excessively. If so, that's a contributor to the problem.

Re: Overcharging on 70 challenger [Re: Mattax] #2745039
02/20/20 08:09 PM
02/20/20 08:09 PM
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I put an M&H engine harness in 15 - 20 years ago. It was good, but not as good as the original. I've repaired and replaced some terminals in more recent years. Glad I saved the original harness to reference and pull connectors from as needed.

Re: Overcharging on 70 challenger [Re: Mattax] #2745132
02/21/20 09:27 AM
02/21/20 09:27 AM
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Abilene, Texas
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The bottom line is he is just going to have to wait till I have a spot for it in the shop. Can’t do this over the phone with his limited skills.

Re: Overcharging on 70 challenger [Re: fastmark] #2746974
02/27/20 09:06 AM
02/27/20 09:06 AM
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Well, we fixed the problem. I finally got a space in the shop for the car so I wanted him to bring me an new alternator and a new voltage regulator, even if they had both been tested good a month before by a really good place. He took the alt and had it tested again at a different place and it tested good again. He bought another new alternator and installed it to check it and have it towed to the shop. Started the car and it’s now working perfectly. The alt shop said they could not test it at a high rpm load so that is where it was overcharging. Sometimes it’s just simple.

Re: Overcharging on 70 challenger [Re: fastmark] #2747029
02/27/20 12:00 PM
02/27/20 12:00 PM
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Omaha Ne
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Thanks for the update beer

Re: Overcharging on 70 challenger [Re: fastmark] #2747069
02/27/20 01:30 PM
02/27/20 01:30 PM
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Rio Linda, CA
John_Kunkel Offline
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The problem with testing Mopar dual field alternators on some alternator bench testers, when hooked up to a grounded field, they will test OK...swapping leads will show the short.


I'm supposed to respect my elders, but its getting harder and harder for me to find one now.

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