Bad Alternator?
 

1970 T/A: Factory volt gauge indicated 13.8 volts with engine running with new battery fully charged. Next day on a test run the factory volt gauge only indicated 12.5 volts with engine running. Put my multi-meter on battery posts with engine running and got 12.5 volts. Took alternator to local auto electrical shop for repair. Reinstalled "repaired" alternator but still same exact results. Is there any other potential issues that would cause a "non charging" condition that I can check for before taking alternator back to repair shop? Car is 100% restored including battery cables, starter, engine wiring harness etc. Also, I took the "repaired" alternator to NAPA for bench test and they said "failed", then took alternator to Oreilly auto for test and that machine said "Pass". Thanks for any ideas.

1970 doesn't that have an external voltage regulator?

1970 and up Firebirds used internal regulators.

I'd say the alternator is not working correctly.
(if it's getting 12 volts to it)

Make sure the connections and fittings are tight. Also check the connections at the starter. (where the voltage comes from)

:confused:

Thanks John, I will check the starter connections today.

You also need the "excitation" to the #1 pin on the two wire connector. In an idiot light car, the alternator gets the excitation through the idiot light. You said that you have a factory voltage gauge, so I assume no battery idiot light and I think they used a resistance wire instead. The other side of the idiot light or resistance would be connected to the ignition switch and active in the on position. To test this, remove the two wire connector from the alternator and turn the ignition switch to the on position without starting the engine. Measure the voltage (from ground) to both of the pins. You should see battery voltage on both of the pins.

I hope this doesn't turn out like your starter stays running problem. Is this the same auto elect shop? In addition to testing the pins as mentioned in post #5, with car running test volts at battery posts then test from bat neg to alt pos post then test from bat pos to alt case for ground reading. Post results

On 10Si alts, if the #2 wire (sense wire ) is not connected, the alt won't work.

George

Yes, this is true, but that would normally make it over charge, not under charge. In my previous post, I suggested that he check both #1 and #2. If #1 is not connected, it will normally not start charging.

That being said, I have read posts (maybe on this forum) where people claim that with #1 disconnected, if you rev the engine to 2000RPM or so it will self excite and start charging and then continue to charge until the engine is shut off. That could explain why it worked one day and not the next. Maybe on the day that it worked, the engine saw some higher RPM before he tested it, and the day that it didn't he tested it right after starting.

The #2 at the plug should be at 12 volts (or battery voltage) all the time, while the #1 would be at voltage when key ON.
(for quick test by unplugging then checking at connector)


Does the Voltmeter gauge in the dash show any voltage when key ON?


:confused:

Test results:

The battery cable to the starter is good and tight!

Post #5 Connector to alt removed, Key on, engine not running=0 voltage at either pin.

Stellar: Yes same electric shop (Only game in town). Test results;
Car running; volts at battery posts= 12.3., Bat negative to alt pos pin=12.4 volts, bat pos to alt case= 12.4 I suppose this means/confirms that alternator is not charging (As my dash gauge indicates)? Thanks

John: volt gauge in car with key off=0. key on=12.5, turn on headlights and volts on gauge drop slightly. This tells me the gauge is working correctly.

Looks like you found it. No power to the plug. See post #5 and #9.

Shermanator2: With the #2 wire disconnected, the Delco 10SI should not work at all. The reasoning for this design is that otherwise, IF the wire is disconnected, the reference voltage for the regulator would be zero, and the regulator would increase the rotor voltage to try to bring up the output, that's how it works normally. The Delco engineers designed it that way to prevent an overcharge condition in case a wire would break or be left unconnected. In an overcharge condition, the idiot lite would be off and if the car had no voltmeter, the driver would never know, and the battery could get hot and explode.

Back when I worked in the biz, our Delco replacement design used an internal diode to keep the output alive in that case, with the output lower by about .7 volts.

George

Ok, Progress. I agree that you have confirmed that it is not charging. We also know that it is not wired correctly. I do not have a wiring diagram for a '70 'bird, do you? What is the history of your wiring harness? Is it original to this car with the gauge package?

As johnta1 says, pin #2 should be always hot. It should connected "electrically close" to the battery positive. This may be at the starter or a junction block on the firewall. This is the electrical point at which the internal voltage regulator will make the voltage "right".

Pin #1 needs to be connected through a resistance to a pole on the ignition switch that is hot with the switch in the run position. As I mentioned, with a car with a "Battery" idiot light, the resistance is the bulb. If the bulb is not there or burned out, the alternator does not start charging, at least at initial idle. You however have a factory gauge package, so I am guessing that this bulb was replaced by a resistance wire or maybe even a physical resistor in the instrument cluster. This is where a factory wiring diagram showing the gauge package option would be really handy.

At this point, just start tracing wires and see why these are not connected.

Ok, this could be. I will admit I have not actually tried it. I was going by memory of schematics of the voltage regulators that I have seen in the past. Maybe those were over simplified or my memory is just oversimplified. Thanks for the correction.

I do not think that the batteries will actually explode when overcharged that way,. just electrolysize the water out pretty quickly. The external electromechanical regulators that are out there right now for 10DN alternators seem to not be made right and are fully overcharging batteries, but that is another story for another thread.

Question for George. Were the motorola VW regs made with the diode also?

The wiring harness from the firewall forward is new and as I said earlier, one day all is good, the next day, alternator not charging! I will take alternator back to the electrical shop in the morning and have them take another look. Thanks.

I am confused now. I thought that you determined that the wires to the connector were not properly connected? If that is the case, the alternator has no chance of working properly and the electrical shop cannot fix it by working on the alternator. Until you correct your wiring problems, you are wasting you and the electrical shops time playing with the alternator.

You said you had 0 Volts on both pins. Sounds like two problems, but may be at the same location. Your engine wiring harness is either defective or not installed properly if you have 0 Volts on pin 2. The problem with pin #1 could be on either side of the firewall, but you need to fix that too.

As I tried to describe earlier, the pin #1 disconnect could possibly act intermittently depending if the engine was reved enough for the alternator to self excite.

If you take the alternator back to the shop and they are tired of you and just want you to go away, they might just reconfigure the alternator as a "one wire", but that is a hack. Hot rodders and tractor guys like one wire because they do not have to connect the other two. This will pacify you and they will get rid of a head ache. Your battery will basically charge and you will go away. Problem is it will under charge your battery if you are running your head lights or other electrical accessories (AC, big stereo etc). If you don't drive at night or use anything electrical, you will not know the difference. The factory did not put the other two wires in because because they had surplus wire to get rid of. As Tom Vought says, engineers do things for a reason. If it were me, I would make it work the way the engineers intended.

This is at the wiring connector plug end? (not on the alternator)

If so, that is not good.

You have the big wire to the alternator connected to the starter terminal?
Should be 12 volts (or battery voltage)

Possibly the wire connections in the 2 wire plug came loose?

:confused: