Charging system

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Eric Pearson

Eric Pearson

73purpule duster
FABO Gold Member
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Good evening everyone, I am having some weird electrical issues. And was wondering if anyone could help. My alternator is putting out a lot of current. I have changed alternator and voltage regulators. Rebuilt the wiring harness triple checked the wiring for proper installation. It puts out upwards of 18 volts at 2000 rpm. And starts to make my volt meter pulse. The voltage regulator is grounded, any help would be greatly appreciated.
 
Let's start at the beginning...

What car
What year
What engine
What electrical modifications



Is the alternator round back or square back

Is the voltage regulator square with one clip on wire and one screw in wire or rectangular with a triangular connector.

How many field wires 1 or 2

I's the regulator grounded
Is the engine block grounded
 
73 duster no electrical mods,square back,2 field wires,grounded regulator triangle connector 408 stroker.
 
1......Determine if alternator field is properly isolated. Remove both field wires and check with ohmeter to ground. field terminals should be low resistance between the two and either should show open/ infinity to ground

2..Determine if green VR wire is OK. This wire goes from one field back to regulator. Disconnect connector from regulator and see if it stops charging. If not, either the alternator field terminal connected to the green is grounded, or the green wire is shorted to ground.

3...Check for voltage drop and grounding.

A...With key in "run" and engine stopped, get your multimeter as close electrically as you can to the VR. This is likely the ballast resistor if you still have one. Do not disconnect any wiring, you want it all connected and drawing current.

Connect one lead of the meter to the key side of the ballast, and stab the other into the POS battery post. You should read a very low value, and if you read more than about .3V (3/10 of one volt) troubleshoot to find where the drop is.

B....Regardless of what you think, actually check the ground of the VR. To do that get the engine warm and running on high enough idle to simulate low/ medium cruise RPM. Stab one meter lead directly into the VR mounting flange HARD. You want to stab through paint, rust, chrome. Stab the other meter lead into the top of the NEG battery lead. As before, you should read very little, the less the better, and zero is perfect

If the above checks out, replace the VR and if that does not help, substitute a known good battery.

If the harness is showing a lot of voltage drop, one way to work around that is to add a relay. Electrically cut the IGN1 "run" wire coming into the engine bay from the bulkhead connector, and use the firewall end to trigger a Bosch relay. Feed the relay contacts power from the starter relay through a fuse or breaker, and connect the load contact "output" to the engine bay end of the cut wire.
 
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ALSO if you do not have a service manual, run over to Mymopar.com and download one free. Some of those manuals GOT THERE because of the guys right here
 
1 field wire alternator


2 field wire ( isolated field)


Testing
 
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Don't square back alt have 3 wires? Round back 2?
 
CRUZE 418 said:
Don't square back alt have 3 wires? Round back 2?
Click to expand...
NO. Isolated field started in '70 and they were still "round back." "Square back" started ?? 72? 73? not sure. Square back generally are better alternators. You can use the isolated field ones on 69/ earlier simply by grounding one field

YOU MUST CHECK every "rebuilt" you buy as the darn things often have ONE FIELD GROUNDED, either purposly or "accidently" due to missing/ incorrect hardware
 
Reason I thought that, when I replaced all of my wiring in my '69, I opted for M&H's electronic ignition plug and play harness. So the old round back 2 wire, voltage regulator and ballast came out for the 3 wire square back, solid state voltage regulator and 4 pin ballast.
 

CRUZE 418 said:
Don't square back alt have 3 wires? Round back
Click to expand...
Technically yes.


Isolated field alts.

Square OR round back
2 wires for field and 1 for power to the battery. 3 wires.

Grounded field alts.
Round or modified square back

1 field wire and 1 for power to the battery. 2 wires


BUT we were only talking about the field wires.
 
LO23M8B said:
If everything failed try a different good battery.
Click to expand...
The reason I said this is because if you have a dead cell but the others are good you're looking at 10.5 volts but the car will start (sometimes) and it will go full field and you'll see that kind of voltage. If you don't have a load tester turn on the headlights for 60 seconds than check the voltage at the battery or go the parts store and have the check it. I have seen this before. 12.7 -12.8 is a good battery.
 
just wanted to let everyone know that I believe that I have figured out the charging system problem. I found that there was only 9 volts going to the alternator instead of 12. Apparently I have some high resistance in the field wire. Thanks for all of you thoughts and advice.
 
If you are talking about the light blue field power wire, that is fed by the IGN1 ignition power feed coming off the ignition switch, "IGN1" coming through the bulkhead, and branching off to feed the field, the VR IGN terminal, the ballast resistor for the ignition, and depending on year/ model, some smog doo dads, etc

There is ONLY ONE "switched" power feed into the engine bay, and that is it. Voltage drop in this circuit often causes OVER chargeing because if feeds UNDER voltage to the VR, "which thinks" the battery is low.


One way to work around this, is to electrically cut the IGN1 wire coming out of the bulkhead, feed the bulkhead end to trigger a Bosch relay, feed the relay contacts power off the start relay, and take the switched load out of the relay and connect that to the other end of the cut wire
 
If you don't have a manual or diagrams they are free for download over at MyMopar
 
I checked voltage at the firewall connector and it was 11. Something volts. Plugged in the connector and checked voltage at the blue field wire at the alternator and it read 9 volts. I wil replace the wire from the connector to the alternator and hopefully it will fix the problem
 
FYI the difference between the 69/ earlier incorrectly called "single field" (grounded field, one field connection) and 70/ later incorrectly called "dual field" (isolated field, 2 field wires) is that.......
69/ earlier, the VR senses battery and controls amount of current going to the alternator field

On the 70/ later ones, the field was controlled by a transistor collector circuit to ground, and so had to be changed. The light blue wire sends key switched full 12V power to the field, through the field, and back to the VR on the green field wire. The VR then controls, so to speak, "the amount of ground" to control field current and therefore alternator output.
 
Eric Pearson said:
I checked voltage at the firewall connector and it was 11. Something volts. Plugged in the connector and checked voltage at the blue field wire at the alternator and it read 9 volts. I wil replace the wire from the connector to the alternator and hopefully it will fix the problem
Click to expand...
It won't. You must troubleshoot with all connections in place. When you disconnected the wire, you lightened the load (current, amperage) on that circuit, so the voltage went up through werever the bad connection is.

The "entire path" is generally as follows, and the drop could be any one or more than one point

From battery to the starter relay "big stud" through the FUSE LINK, through the BULKHEAD CONNECTOR via the BIG RED ammeter wire, to the AMMETER, through it and out on the BIG BLACK ammeter wire, to the WELDED SPLICE which is a few inches from the ammeter, under the dash.

The WELDED SPLICE branches off and feeds power to the IGNITION SWITCH, through the SWITCH CONNECTOR, SWITCH, back out the SWITCH CONNECTOR on the (usually blue) IGN1 ignition feed.

That wire feeds back into the engine bay through the BULKHEAD CONNECTOR and branches off to feed the ignition ballast, VR, blue field wire, etc

ANY ONE of the capitalized points can be a drop. You need to "chase it back" to find it

As I said earlier, adding a relay can help in most cases
 
Eric Pearson said:
I wil replace the wire from the connector to the alternator and hopefully it will fix the problem
Click to expand...
It could if the wire had broken strands in it.

Ie if the wire has 12 strands and 9 we're broken then all the field current has to go through the 4 strands and there would be a tremendous resistance at that point under load. Not sure it would account for 3v voltage drop
 
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