Alternator question

I just bought a 1986 Carrera targa. 165,000 miles.
The PO Told me the alternator is going or gone. He can get me a new one for cost.

But, I have a question about the alternator light.

WHile driving with the light son last night it tried dying until I turned the lights off, so once the load was reduced on the battery / charging sytem, it ran better.
The alternatoer light did not come on, which was odd... SHould that light off been on?
I do plan on checking the Grounds on the body and engine and trans.

The PO said something about damaging the alternator while Jumping hte car, does that sound like it could happen.


Thanks again in advace for any help.
Bruce

1986 targa Carrera
1965 911, work in progress...

Yes, the warning light should have been on if the system Voltage was below spec. Get a new bulb and a spare, as I believe all of the dash warning lights use the same bulb. Some alternators -- specifically the one's with an external regulator, will not operate without a good bulb in the circuit, as it is used to provide excitation current for the armature winding.

An alternator can be rebuilt locally for around $100 if it turns out to be malfunctioning, a lot better deal than a replacement at 3-4 times that cost!

After you get the warning lamp replaced, you need to check the system operating Voltage with a digital multimeter ... it should be 13.5 to 14.5 Volts at any engine speed above idle. Any less than that means your alternator needs servicing, because it has an internal regulator, not easy to check in the car. Anything above 14.5-15 Volts means your regulator is bad and servicing, too!

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Warren Hall
1973 911S Targa

Does the alternator light come on when the ignition is on but the engine is not running? - If not suspect a blown bulb or a broken connection between the alternator and the starter motor. Also check the voltage at the battery with the engine running. From memory 13.8 - 14.5 volts would indicate a working alternator and connections.

As far as I am aware alternator damage would only occur if connections were made wrongly when jumping the car, and there would probably be other problems as well

Good Luck

Roy M

Thanks guys...

I just read over all the other ALternator posts and took several notes, I will check everything tonight after cahrging the battery, I will charge it out of the car.

I do not remember if the Light comes on with the ignition wire on.

Can someone tell me the proper Light bulb I need so I can pick it up onthe way home, Nearest Auto Parts about 8 miles.

Thanks
Bruce

I got home with a new bulb, wrong one of course...

The bulb is good, checked with an digital Ohm meter.

Charged battery, reads 12.1 volt, with car running, 12 volts.
SO the alternator is not working.

I will check the wires to the STarter next, I did clean the contacts of the aternator and the lplug that plugs into the panel inside the rear drivers side quater.

Any other suggestions..

I'll update on the starter wire soon, I hope, heading back out now..

Bruce

Well, it sounds like you know what you're doing and I'm wondering if you had to get to the back of the alternator to "clean the contacts." A longshot as it looks like these alternators might be hard to get at. At any rate, what I'm saying is if you can get the alternator out, take it to a shop that can test/rebuild it. the cheapest and best option, as Warren points out.

I believe you also know that the car is draining your battery and will not go far if you drive it.

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'83 SC

Superman

Yes, it sucks to have a new toy and not be able to play with it..

I have not taking it out of the driveway since I got it home.

I got the alternator out and will bring it to a shop tommarow or get a rebuilt one.

Thanks
Bruce

It sounds as if the alternator is not putting out enough of the batter is not capable of charging via the alternator. Try the following to determine if the alternator is putting out enough juice:
1. Start the motor,
2. With motor running, disconnect the positive battery terminal,
3. Does the motor continue to run, if yes go to 5,
4. If motor stops, the alternator is not putting out enough power to run the electrical system. Most likely the problem will be the alternator.
5. The alternator is putting out enough juice. Check out the rest of the electrical system. It could be your battery is bad because it cannot hold a charge.

Your point 2 gives me a chance to ask a supplemental question. It has always been drummed into me that you NEVER allow an alternator to run on open circuit - it will be destroyed. However, when my connection between starter and alternator failed, mine was on open circuit for a good period of time yet the alternator was fine.

Anyone with the knowledge and / or experience to sort out the myth from the fact?

Thanks

Roy M

I took the alternator to a shop today, they called later and said it had a bad stator, the inside part that turns, and a bad regulator.
So they are going to replace those parts and the Bearing, and hopfully I'll get it back tommarow.
It will cost around $160.00..

I will update after I get it back in tommarow.

Thanks again for the help.

Roy, I've been disconnecting the battery cable to check if the alternator is functing for over twenty years on cars from jap imports, mercedes, english (sucky electrical systems) to american mustle cars and of course, my porsche - 78 SC. I have NEVER had any problem with the alternator being destroyed by such testing. In fact, the testing is always proof positive if the alternator is putting out a charge. Your own experience should be proof. If the myth was correct, your alternator would have been fried! But if anyone knows different I am willing to listen. 65-911 how did you finally narrow it down to the alternator?

pbs911
For one thing the PO told me it needs an alternator, but I was hoping he was mistaking and it was a loose connection.
I took the suggestions of the other posts.

Checked the voltage at the battery it stayed around 12 volts before starting the car and after starting the car.

And the battery was getting lower and lower, so I had to charge it, and did not drive far.

I also checked and cleaned the grounds on the tranny and engines etc.

The thing that thrugh me off was the Alternator light not working...
Maybe the reason it was bad was beacause the stator was bad in the alternator and not completing the path for the electricity.

It will be interesting to see if the alternator light is working with it repaired.

I did check the bulb and it was good.

Thanks
Bruce

I got the rebuilt alternator today, thought I was going to get it yesterday, but the shop did not get the parts in until today.

It works, the Alternator warning light comes on until I start it, and the voltage going to the battery goes up to 13.8 - 14.2 volts.

The tach still does not work. But that is a different thread.

Thanks for all your help.
Bruce