[george kujanski]

Stellar: I think the added diode was a feature they kept in all of their aftermarket/ 10SI-type alts with internal reg. In fact, I have a Motorola Delco 10SI replacement alt (Engineering sample) on my GTO. I can easily confirm that's the case on the one I have.

George

[dpoltzer]

Sorry for confusion but here are test results that I just did again and hopefully with better descriptions:

Key off:
The main power terminal on the back of the alternator which has a 10ga wire on it that goes in to the engine harness and gets to starter for its power:
Voltage=12.2

With the two-wire connector that plugs in to the top of the alternator, (It plugs in to the two blades of the internal voltage regulator) plugged in, I can probe each of these wires. The black wire which is above the #1 on the back of the alternator case, the voltage = 0
The red wire which is above the #2 on the back of the alternator case, voltage = 12.2

With key on and motor not running:

Main power terminal = 12.2volts #1 black = 3.3 volts #2 red=12.2 volts

Sorry again for the confusion.

[johnta1]

That sounds better. (for the wiring )

Maybe the regulator in the alternator is going bad, now is bad?

These aren't that hard to do, they sell the parts for them.
(were pretty cheap)

Is your alternator a "numbers" matching alternator?

[shermanator2]

Originally Posted by dpoltzer

Sorry for confusion but here are test results that I just did again and hopefully with better descriptions:

Key off:
The main power terminal on the back of the alternator which has a 10ga wire on it that goes in to the engine harness and gets to starter for its power:
Voltage=12.2

With the two-wire connector that plugs in to the top of the alternator, (It plugs in to the two blades of the internal voltage regulator) plugged in, I can probe each of these wires. The black wire which is above the #1 on the back of the alternator case, the voltage = 0
The red wire which is above the #2 on the back of the alternator case, voltage = 12.2

With key on and motor not running:

Main power terminal = 12.2volts #1 black = 3.3 volts #2 red=12.2 volts

Sorry again for the confusion.

OK, this does make more sense, but what I still want to know is with the plug disconnected from the alternator and the key in the run position (but engine not running), what is the voltage on terminal 1 of the connector?

[stellar]

dpoltzer- I think a trip back to the elect shop is in order. The wiring sounds good.
shermanator2- I would also like to know the voltage with the plug removed from the alt. I suspect it will be 12 at both. Years ago, I had an alt on the test stand and was able to energize the field at #1 reg pin with a D cell battery which is about 1.5 volts so I think if the alt was good it should work with the 3.3 volts connected.
George, is that a 9RC2040 reg on your alt? They are getting hard to find. Are they still available?

[dpoltzer]

Test results: Connector disconnected from alt., key on, volts at the black # 1 wire = 12.4. (Battery tender has been on all night). So this seams to indicate that voltage is flowing thru wiring and that the voltage regulator is not working?

This is a 1970 open face alternator which is why I want to keep it. Thanks everyone.

[shermanator2]

Originally Posted by dpoltzer

Test results: Connector disconnected from alt., key on, volts at the black # 1 wire = 12.4. (Battery tender has been on all night). So this seams to indicate that voltage is flowing thru wiring and that the voltage regulator is not working?

This is a 1970 open face alternator which is why I want to keep it. Thanks everyone.

I agree now that it is something internal to the alternator. It might be the voltage regulator, but it could also be something else like an open rotor.

I am glad you are keeping your original alternator. I wish everyone did. They are usually easy to rebuild and parts are available. Hopefully your local shop is competent enough to do so.

[dpoltzer]

Thanks much! What does an open rotor mean exactly? Dave

[shermanator2]

Originally Posted by dpoltzer

Thanks much! What does an open rotor mean exactly? Dave

Open means it no longer has electrical continuity. The wire has broken somewhere or is no longer connected to the slip rings. Electrically the rotor is just one continuous coil of wire going from one slip ring to the other. In order to control the output voltage, the voltage regulator controls the current in the rotor. If the rotor is an open circuit, it can have no current, and therefore the alternator will have no output.

I am not saying that this is necessarily the problem, just that it is one possible problem other than the regulator.

[dpoltzer]

I really appreciate your information! I will take alternator back to shop and have them open it up again. I will let you know. Dave

[dpoltzer]

Took alternator back to shop and they confirmed that it is not charging!! They suggested that I have another wiring issue such as a bad fuse or loose wire in the fuse block that caused alt. to go bad. I just checked every fuse visually and also used test light on either side of every fuse and they are all good. I still think that they never rebuilt/fixed the alternator the first time I took it there for repair. I will pick up the repaired alternator later today hopefully and will report back.

[shermanator2]

Originally Posted by dpoltzer

They suggested that I have another wiring issue such as a bad fuse or loose wire in the fuse block that caused alt. to go bad.

They are full of $h!t

[dpoltzer]

I do believe your assessment is correct! THX.

[dpoltzer]

Picked up alternator and they replaced the voltage regulator and the Armature windings. They said the windings were shorted out and suggested that some issue with the car wiring was the cause ???? No charge though. Tonight I will install the alt and will check for voltage to #1 & #2 before even plugging in the connector (Only the power 10 ga. wire will be attached) both 1 & 2 should have 12 volts with key on, right? Dave

[shermanator2]

Originally Posted by dpoltzer

both 1 & 2 should have 12 volts with key on, right? Dave

Correct

[dpoltzer]

Results, With key on and wire connector un plugged, battery hooked up: 12.5 volts at battery and also at power lug on alt. 12.5 volts at the #1 & #2 wires on the connector. Zero volts at either of the voltage regulator spade connectors!!! I thought they should both have 12.5 volts??

[stellar]

What you have is correct. There should be no volts at reg pins with plug out. Only at the plug. Everything sounds good. Fire it up!

[dpoltzer]

Fired it up and we have great voltage everywhere including at battery and voltage gauge in car!! Thanks again everyone for all of the great assistance. Dave

[Jack Gifford]

So...
Apparently whatever it was in the car that killed the alternator must have magically fixed itself...

[dpoltzer]

Exactly! I believe that was a C.Y.A. comment by the shop owner as I believe that they "forgot" to even open up my alternator!