Voltage over 15 volts at all times. Stumped, see diagnostic list.

[72sunroof]

Okay I have been chasing this for 2 months.
It is a 72 Charger with 70 amp alternator square back 2 field
Fully replaced engine wiring harness when restored 10 years ago
Replaced the bulkhead connector last year
Replaced the ignition switch and fixed al the connections {did this today}
Checked continuity from field wires to regulator ok
Checked continuity from blue field to blue on ballast ok
Checked continuity between fields ok
Checked voltage reading between blue wire in ballast and battery in run it is high 1.3 volts both before and after changing ignition NOT OK
Have tried 2 different regulators 1 is new Mopar reproduction with modern guts other is 1972 known good regulator both have great grounds
Wires are tight on amp gauge
Have a bypass helper wire from alt output to battery connection at starter relay 10 gauge with a fusable link.
Firewall has ground strap to back of engine
Even tried a known good 40 amp alternator same result
Where else to look?

 

[pnora]

Bad plug on regulator.

 

[bearman]

What size pulley on the alt. Can replace with larger and slow it down. Just a thought

 

[72sunroof]

Bad plug on regulator.

Nope checked continuity

 

[72sunroof]

What size pulley on the alt. Can replace with larger and slow it down. Just a thought

Was doing 13. Volts with same alt and pulley

 

[pnora]

Nope checked continuity

Ok you have the answers but its not fixed. It is a simple system.

 

[72sunroof]

Just checked blue field wire to ground had continuity
Removed bulkhead connector NO Change
Pulled off alternator it went away
Checked that field to ground, yep it is grounded. But does that mean the other alternator also grounded internally

 

[4406bbl]

At this point heat up the regulators with a heat gun and see if the voltage goes down, they should temperature compensate. I just returned 2 standard ignition regulators that would only get down to 15.03 volts hot, I had to get an adjustable regulator. It can still be the alternator.

 

[72sunroof]

Ok you have the answers but its not fixed. It is a simple system.

I have no answers except that the blue field connection is grounded and a known good alternator gave me the same voltage . And it is not that simple.

 

[pnora]

I have no answers except that the blue field connection is grounded and a known good alternator gave me the same voltage . And it is not that simple.

First of all the blue field is not grounded. It is a the keyed 12 volt feed and sense wire for the regulator. Continuity means nothing if you do not know how the system operates. Remove blinders.

 

[68 Sport Satellite]

Had same thing happen to me when running a 70A alternator. Install an adjustable voltage regulator and all will be good. Do it soon before you fry some of your gauges. Mine ran normal voltage for a few months then was 15V like yours. I thought my voltmeter (converted from Ampmeter) went bad. Nope. The voltage was correct. It fried my fuel gauge and temperature gauge and I thought for a while I had an overheating condition. Adjustable voltage regulator is needed with that alternator current.

 

[4406bbl]

One other thing I do since parts are junk now is I have a harness I replace the original regulator harness with for testing. Blue to the battery, center post on regulator, and one field, green to outer post on regulator and the other field, this eliminates all other wiring and let's you find the issue, at that point it can only be battery, alternator, or regulator. So essentially you build a harness like the pic, and where the blue wire hooks to the ballast goes to the battery, for testing. If you want to make your system better you can relay the blue wire to the battery and trigger the relay with the original regulator blue wire, no voltage drop worries ever then, you must fuse or fuse link your battery wire, 10 amps max.
.

 

[toolmanmike]

Did you test the battery? Never overlook the obvious.

 

[4406bbl]

And a battery that tests good can still cause this.

 

[72sunroof]

Did you test the battery? Never overlook the obvious.

And a battery that tests good can still cause this.

It is an AGM that is showing 12.67 volts and passes load test.
I honestly think it is this rebuilt alternator the field wire is grounded in the alternator variable voltage regulator is just covering up an issue. I have had a normal set up for 35 years it just went wacky.

 

[70bigblockdodge]

I would try another voltage regulator. Beyond that I would look at battery connections. Something it signaling the regulator to charge when it should be relaxing. A voltage drop somewhere or a internal failure in a component.

 

[toolmanmike]

Okay I have been chasing this for 2 months.
It is a 72 Charger with 70 amp alternator square back 2 field
Fully replaced engine wiring harness when restored 10 years ago
Replaced the bulkhead connector last year
Replaced the ignition switch and fixed al the connections {did this today}
Checked continuity from field wires to regulator ok
Checked continuity from blue field to blue on ballast ok
Checked continuity between fields ok
Checked voltage reading between blue wire in ballast and battery in run it is high 1.3 volts both before and after changing ignition NOT OK
Have tried 2 different regulators 1 is new Mopar reproduction with modern guts other is 1972 known good regulator both have great grounds
Wires are tight on amp gauge
Have a bypass helper wire from alt output to battery connection at starter relay 10 gauge with a fusable link.
Firewall has ground strap to back of engine
Even tried a known good 40 amp alternator same result
Where else to look?

You might want to read through this thread. Diagnosing high voltage

 

[dvw]

Continuity doesn't check the circuit for integrity under load. To do that you need to do a voltage drop test. Set the meter set to DC volts. One end directy to the negative battery post. The other end to the ground you wish to test. Such as the regultor itself (not the mounting bolt). Then watch the meter. it shouldn't go over .5 volt while the failure is occuring. The hot side can be checked the same way. Positive battery stud to the output stud at the alternator. I'm going to discount the alternator or regulator since you have substituted other parts. Either there is a grounding issue at the regulator case. A poor connection between the alternator output stud and the battery. The "F" circuit is rubbed thru to ground. The "I" circuit has voltage is fluctuating. I worked at the FCA electrical lab 9 years debugging prototype vehicle electrical issues. Saw plenty of poor crimps, heat shrink glue seeping into terminals, poor grounds that were tight and showed low resistance when measured with an ohm meter.
Doug

 

[toolmanmike]

.

 

[Sixpactogo]

It is a simple system. If you have 16 volts going to your system, the voltage is not being properly regulated. The alternator will put out at least 17 volts if working properly and it is the regulators job to drop it down to 13.4 - 14 volts. It appears to me that everything is doing its job except the regulator.
That said, I would make sure the regulator case is grounded properly by testing with a digital ohm meter between neg post on the battery and the regulator case. Better be less than .02 ohms. With a good ground and still allowing more than 14 volts to the system, there is no other culprit to blame IMO.