Alternator or voltage regulator?

[djcondie]

I have a 1982 911sc whose battery is not being charged. How do I determine if it is the alternator or the voltage regulator that is not working? When I turn on the key without starting the engine the battery light does not come on and it used to.I put a volt meter on the electrical system with the engine running and it showed only 7 volts. What other tests are that I can run? Thanks for any advice, Dave

[T77911S]

the bulb may be burned out. it has to have a good bulb for the charging system to start charging

[wwest]

Originally Posted by djcondie

I have a 1982 911sc whose battery is not being charged. How do I determine if it is the alternator or the voltage regulator that is not working? When I turn on the key without starting the engine the battery light does not come on and it used to.I put a volt meter on the electrical system with the engine running and it showed only 7 volts. What other tests are that I can run? Thanks for any advice, Dave

Under the conditions you describe I would be suspicious, first, of the voltmeter or the point of measurement. It seems improbable that the car would run on as little as 7 volts.

You don't say the miles but the slip ring brushes would be my first guess. By this MY the bulb had a parallel resistor to overcome the problem of a failed bulb. On the other hand he brush failure isn't generally a "sudden" thing, lots of "blinks" of the bulb leading up to failure.

[djcondie]

I will check the bulb, thanks

[djcondie]

I forgot to mention that the battery is about 6 years old, it seems to hold a charge when I use a battery charger. The tach was flopping back and forth when this problem happened yesterday.

[mysocal911]

Originally Posted by T77911S

the bulb may be burned out. it has to have a good bulb for the charging system to start charging

That's critical!

[djcondie]

I checked the bulb and it is good. Any ideas as to why it is not lighting up?

[timmy2]

Voltage regulator failure or the blue wire is making a poor connection or has come off.
Remove and clean the 14 pin connector at the rear of the engine fuse panel and see if it comes on.
Blue wire runs from back of alternator to 14 pin connector to alternator.

[mysocal911]

Originally Posted by timmy2

Voltage regulator failure or the blue wire is making a poor connection or has come off.
Remove and clean the 14 pin connector at the rear of the engine fuse panel and see if it comes on.
Blue wire runs from back of alternator to 14 pin connector to alternator.

After that, it's time to access the alternator and ground the blue wire at the alternator.

[djcondie]

I cleaned the 14 pin connector and still no light so I will check out the blue wire on the alternator and ground it. Thanks for the advice.

[timmy2]

Did you test for continuity from the blue wire at the gauge to the 14 pin connector?
Do the same test from the back of the alt to the gauge.( with 14 pin connector plugged in)
If all good the I would suggest it is a problem with the alternator.

[djcondie]

I'm not sure what gauge you are referring to.

[Targalid]

djcondie,
This is how I did my diagnosis and repair. I plugged a volt meter into the cigarette lighter. Then I drove the car while carefully watching the voltmeter. According to other posts on this forum, voltage spikes above 15 volts indicate a failing voltage regulator. I saw spikes as high as 17 volts while driving. I replaced the 37 year old Marchal voltage regulator with a new Huco solid state unit. I still had charging problems. I then focused on the 14 pin connector, still watching the voltage meter in the cigarette lighter. With an assistant watching the meter, I tested the various wires in the 14 pin connector. When I moved the blue wire, pin 11 as I recall, the charging circuit either worked or not depending on the wire's position. I replaced my cracked 14 pin connector plastic housing, cleaned all the connections therein before reassembly and I have been charging perfectly ever since.

[djcondie]

Thank you for the information. I will focus on that today.

[timmy2]

Charging Lamp wiring at the gauge is what I was referring to.

[wwest]

Originally Posted by Targalid

djcondie,
This is how I did my diagnosis and repair. I plugged a volt meter into the cigarette lighter. Then I drove the car while carefully watching the voltmeter. According to other posts on this forum, voltage spikes above 15 volts indicate a failing voltage regulator. I saw spikes as high as 17 volts while driving. I replaced the 37 year old Marchal voltage regulator with a new Huco solid state unit. I still had charging problems. I then focused on the 14 pin connector, still watching the voltage meter in the cigarette lighter. With an assistant watching the meter, I tested the various wires in the 14 pin connector. When I moved the blue wire, pin 11 as I recall, the charging circuit either worked or not depending on the wire's position. I replaced my cracked 14 pin connector plastic housing, cleaned all the connections therein before reassembly and I have been charging perfectly ever since.

That doesn't seem to explain the 17 volts spikes....If you read them on a digital meter then they had to be a bit more than "spikes"....