Severe voltmeter needle oscillations

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I see some questionable things here. Perhaps you already fixed them.


The lower yellow circle appears to be the green field wire disconnected.

The upper yellow circle appears to be the field post it might go on

The magenta circle looks to have a connector on it but soldered to the output charge wire

The green circle is the output charge wire from the alternator to the battery
Screenshot_20230607-194908.png


Don't know what is going on there.

The typical square back uses 2 field wires, one is full battery voltage the other comes from the electronic voltage regulator


There are square back alternators that have been modified by grounding one terminal and work with the old electro mechanical regulators.

This is where what voltage regulator you have is super important.
 
Hi Danadart

Here's a today pic of my alternator :
20230608_111750.jpg

The green and blue wires are original and a little bit damaged, but I tested their continuity with the VR : OK.


My VR is made in China. I think it's a fully electronic one.
20230608_111942.jpg


20230608_112004.jpg


20230608_112017.jpg


Today, I made some measurements

Battery engine off : 12.6v
Battery engine on (at idle) : 12.7v
Battery engine on (revving) : 14v~15v
Fusebox and fuses OK

I removed the alternator belt and tried driving on the battery alone : no change, the problem is still there.

I also tried to connect the voltmeter onto a permanent (BATT+) at the fusebox : the needle doesn't oscillate anymore and read 14 volts (a bad contact into the ignition switch? I will check the connector)
But the problem of T/S and wipers remains. They do not work while revving and driving, and are back as soon as I shut off the engine.
Something in the charging circuit cause a problem, but what???

I wonder if I won't go back and reinstall an ammeter :rolleyes:
 
Last edited:
French demon said:
I wonder if I won't go back and reinstall an ammeter
Click to expand...
If you disconnected your voltmeter and the problem still exists, that's not your problem.

If the Ammeter wires are cleanly connected to each other and insulated, that's not you problem either.

You said that you took the belt off................. @Dana67Dart suggested removing and insulating the field terminals. This would electrically disconnect the alt from the system. The alt would still be fed with the belt off (sorry, just spitballing)
 
Hi Troy :) Some news of your Demon?

IMO, an alternator isn't fed. It is it which sends current to the battery, not the contrary.
I think that disconnecting the terminals or removing the belt causes the same effect : preventing the ALT to send current into the circuit. Am I wrong? I don't know... @Dana67Dart will tell us.

François
 
I was low on fuel, so I went to the gas station.

On the road to go to the station, my voltmeter was on "0" and no turn signals.
But on the way back to home, it was on 15v and the turn signals were working.

This car is haunted :mob:
 
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French demon said:
Hi Troy :) Some news of your Demon?

IMO, an alternator isn't fed. It is it which sends current to the battery, not the contrary.
I think that disconnecting the terminals or removing the belt causes the same effect : preventing the ALT to send current into the circuit. Am I wrong? I don't know... @Dana67Dart will tell us.

François
Click to expand...
I just figured that if you had an issue in the field circuit (fed circuit), that may be causing your anomalies. Disconnecting those would take the field circuit out of play.
 
French demon said:
I think that disconnecting the terminals or removing the belt causes the same effect : preventing the ALT to send current into the circuit. Am I wrong? I don't know
Click to expand...
Removing the belt stops the alt from spinning BUT the field wires are still hooked up and the field is drawing current.

By disconnecting a field wire the field is no longer drawing current.

From the looks of those wires I would not trust any of them.

Still your symptoms do not point to the charging system they point to bad wiring somewhere in the system.

The VR and the alternator match so that is good BUT you should check that the alternator is really an isolated field alternator.

Easy check... Disconnect both field wires from the alternator.

With a multi meter check to see if there is resistance or open or short to ground from each terminal and ground.

In an isolated field alternator both field wires should have no connection to ground ( many meters display this a OL, basically what the ohm meter reads when the leads are not touching each other.)
 
François, have you obtained a wiring diagram for your car?

That is utmost important for you to understand what's happening.

I think the issue is not time or distance related but vibration.

A bad connection might work but one little bump or vibration and can brake the connection.

I had one dash lamp that would come on and off, it was just a bad connection, I bent the tabs a bit forcing a tighter connection and no more problem.

The bulkhead connectors are the same. If not tight enough they can not pass enough current to run things.

Even in that state they might show 12 volts but when a load is applied they will be to high a restance to provide the device enough currently.
 
Yes, I have the wiring diagram for '71 Dart/Demon
I also think I have a bad connection somewhere because sometimes the voltmeter needle goes down when the car pass onto a road irregularity, or a speed bump.
But where??? Hard to tell, especially behind the dashboard. My bulkhead is in a really good shape and clean (I replaced all male prongs on the engine side harness)

I recently installed a new (but used) untouched 1971 dashboard harness. My original one was in a very bad shape, with a lot of cuts, splices, wrong color wires... This replacement harness came from a FABO member (Troy "CFD44"). Thanks a lot to him.
I tested all wires continuity of this harness before installing it. It's OK.
Demon '71 resistor with legend.jpg


On the other side, my turn signal switch is a reproduction. Sometimes reported as junk :rolleyes:
And my ignition switch connector had been cut by a previous owner. I had to recreate the connection wire by wire to match the car connector :
20220503_202757.jpg

All this works.... but?

I would prefer to have original Chrysler T/S and ignition switches, but these parts are logically unavailable in Europe and expensive to import from States. :(
 
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Francois, I am thinking that you have a problem with your ignition switch and/or associated wiring. There is a welded splice under the dash that contains the battery, alt, amp gauge, headlight wires AND ignition switch feed. Once in the steering column, there is an accessory feed in the harness that that sends power out to a smaller splice. This smaller splice feeds the wipers, accessory terminal (where your gauge is plugged in)on the fuse block and the 12v dash supply (I suspect that your gauges don't work with the rest of the aforementioned deficiencies). If it were me, I'd wedge a test light into the back side of the 12 gauge black wire coming from the ignition switch (on the vehicle side of the plug) and go for a ride. When the voltmeter is reading voltage, the light should be on. When the voltmeter goes to 0, the light would be off. To me, this would indicate the problem with the feed coming from the ignition switch.

Take my suggestions at your own risk :)

Good luck
 
You and Dana67Dart are right. I've a bad connection somewhere.
Thank you Troy for giving me a clue : the 12Ga black wire of the ignition switch.
I'll check it tomorrow :thumbsup:

François
 
Also you replaced the engine side spade connector in the bulkhead but did you tighten up the female side of the dash harness in the bulkhead?
 
Dana67Dart said:
Also you replaced the engine side spade connector in the bulkhead but did you tighten up the female side of the dash harness in the bulkhead?
Click to expand...

Honestly no. The female side of the bulkhead connector, on the dash harness, was (and still is) in a very good shape.

If tightening the I/S connections doesn't resolve the problem, I will have a look there.

It would be ideal to find an OEM ignition switch connector like this one :
IS order.jpg

The best way to improve my I/S connection

Maybe I'm going to restore a good connection with an aftermarket male/female connector.
This implies installing a connector onto the I/S switch, but also onto the main wiring harness.
Connectors.jpg


or this one (maybe easier as the wires are already plugged in) :
Connectors 2.jpg



François
 
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Well, after having checked the I/S switch connector and wires = ok.
The bulkhead connector = ok.

I think I've found the guilty = the turn signal switch.
As I told before, it's a reproduction (probably made in China). And often reported as junk.
I confirm.... IT'S JUNK... :mad:

When T/S doesn't work (and the voltmeter drop to "0"), if I slightly pull on lever toward me, miracle... T/S starts working again (and the needle stays on 13 volts).
Bad contact somewhere into the switch, and this causes a mess in the circuit.

I need an OEM T/S switch.
 
French demon said:
Well, after having checked the I/S switch connector and wires = ok.
The bulkhead connector = ok.

I think I've found the guilty = the turn signal switch.
As I told before, it's a reproduction (probably made in China). And often reported as junk.
I confirm.... IT'S JUNK... :mad:

When T/S doesn't work (and the voltmeter drop to "0"), if I slightly pull on lever toward me, miracle... T/S starts working again (and the needle stays on 13 volts).
Bad contact somewhere into the switch, and this causes a mess in the circuit.

I need an OEM T/S switch.
Click to expand...
Good job, glad that you found it. Intermittent problems are the worst. :thumbsup:
 
Thanks, Sirs.
As Chrysler OEM T/S switches seem to be gold plated (circa $200.00), I will try to disassemble mine and see if I can resolve this problem...
 
Carburetted vehicles had a voltage regulator that controlled the field current. Some controlled the volts to the fiel and some controlled the ground.
You can measure the voltage to the regulator and with a DMM the Hz or frequency.
Your problem could be the regulator, but I would suspect worn brushes. Worn brushes have low spring force holding the brushes to the slip rings. Any out of concentric or also probably present loose bearings allows the armature to jump around as the revs come up, causing the brushes to make and lose contact. This is RPM related.
 
67Dart273 said:
Here, generally is what the problem might be, in no order:

1....As I mentioned, a poor designed voltmeter
2....Voltage drop in the harness, which can include bad connections of any kind, in the bulkhead connector, the ignition switch connector, the switch contacts themselves, or partial failure of the big master splice in the black ammeter wire
3....Poor grounding especially the VR
4....In rare cases a bad VR
5....In rare cases something with the battery, perhaps sulfation.


I assume you have a mostly factory harness, and still have the bulkhead connector. Voltage drop from several sources, and sometimes a combination of them, can cause this. With what you describe, if it is NOT a bad voltmeter, you should be able to "see" this in the headlights/ or dash lights with the parking lamps on

One thing I recommend, because of voltage drop problems, is to add a relay to operate ignition "run" buss loads which then gives the VR a stable voltage.

Electrically cut the ignition 1 "run" wire coming into the engine bay out of the bulkhead. This is NOT fused originally, and feeds the ignition system, VR, and alternator field. On some cars it feeds electric choke and maybe some smog doo dads.

Take the bulkhead end of the wire and use it to trigger a bosch relay. Feed the relay contacts with a fairly large, IE no 12 ga through a fuse / breaker from the start relay "big stud." Connect the load contact to the engine bay harness end of the "run" wire you cut.

Also make REALLY certain the VR is actually grounded. I like to run a big jumper from the engine to the body, and in original form, this is pretty minimal.
Click to expand...
An ampmeter is slow in response. If the alternator or generator quit output they will go to negative output indication quickly. The same on start. They will indicate positive output for a few minutes as the battery is recharged. So quick fluctuations of output current will not show up. A volt meter gives quick indication of fluctuating output. When the alternator is charging the voltage will be up. When it is not charging the voltae indicated will be up.
 
You may have inadvertently loosened or broke wire or other connections when you messed with the fuse box. I took my fuse box out to add power locks and when it was all put back together I lost the gas and temp guages. I went back and reinstalled the fuse box and everything started working again. Why you're in there look for frayed wiring which can ground out. You'll find it, hang in there.
 
Dale Davies said:
An ampmeter is slow in response. If the alternator or generator quit output they will go to negative output indication quickly. The same on start. They will indicate positive output for a few minutes as the battery is recharged. So quick fluctuations of output current will not show up. A volt meter gives quick indication of fluctuating output. When the alternator is charging the voltage will be up. When it is not charging the voltae indicated will be up.
Click to expand...
No voltmeter should cycle as he describes.
 
Dale Davies said:
Carburetted vehicles had a voltage regulator that controlled the field current. Some controlled the volts to the fiel and some controlled the ground.
You can measure the voltage to the regulator and with a DMM the Hz or frequency.
Your problem could be the regulator, but I would suspect worn brushes. Worn brushes have low spring force holding the brushes to the slip rings. Any out of concentric or also probably present loose bearings allows the armature to jump around as the revs come up, causing the brushes to make and lose contact. This is RPM related.
Click to expand...
He was sayin earlier that the voltmeter still cycled with the alternator disconnected or I thought that is what he said
 
French demon said:
Well, after having checked the I/S switch connector and wires = ok.
The bulkhead connector = ok.

I think I've found the guilty = the turn signal switch.
As I told before, it's a reproduction (probably made in China). And often reported as junk.
I confirm.... IT'S JUNK... :mad:

When T/S doesn't work (and the voltmeter drop to "0"), if I slightly pull on lever toward me, miracle... T/S starts working again (and the needle stays on 13 volts).
Bad contact somewhere into the switch, and this causes a mess in the circuit.

I need an OEM T/S switch.
Click to expand...
The TS switch should not cause this problem if you are not using the TS
 
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