alternator light doesn't go off completely.
 

I figure that I need to start by changing out the voltage regulator. Connections all look good. Am I on course?

What year 911? The longhoods light always glows a bit dim. Hard to see during the day, but you can see it at night.

'71

Make sure the belt tension is correct. Things might be slipping.

Bob

My 72 does this also boy it drives me crazy too, is this really the norm??

I think it's very common. My '68 does it as well.

No intention to hijack here, but my '84 is doing this too. The light stays on kind of flickering until about 2.5k. Sometimes it goes away after giving the engine a quick high rev. But it has consistently stays on every time after startup. I haven't checked the connections in the back yet. Loose ground?

Not to make anyone feel like their vehicle "sucks" but your light should not always be on. My 66 turns on when there is actually a low voltage situation. When my battery is low when cranking it may come on from time to time. I would start with the battery. It could be on its way out. Also could be belt but you would notice a pretty shiny glossy belt and could probably hear it slip.

I am by no means an expert. but .... I did have a flickering light on my 87. I had the alternator replaced and the problem went away. FWIW.

My light comes on bright below 2000 rpms and goes to very dim above.

I did take it to the mechanic and he said the alternator is putting out around 14V; no problem there. But, either the voltage regulator has gone south (he recommended changing this out first to rule it out), or one of four diodes in the alternator has failed.

He launched into this AC to DC conversion thing that was over my head. But, what I took away was that the system will continue to work, but that if another diode were to fail (or something along those lines) that the AC current could damage the ignition system.

So his recommendation was start with the voltage regulator. And then, if that doesn't fix it; move on to replacing the alternator.

Using the alt. light as a diagnostic tool:

1. no light with ignition "on" not running
a. bad regulator
b. bad light
c. open slip rings
d. bad brushes

2. light stays "on" with key "off" - shorted diode/diodes

3. light glows brightly while running
a. open diode/diodes
b. shorted rotor/stator winding
c. shorted alt. light wire to ground
d. bad regulator

4. light glows dimly & gets brighter with higher RPMs - voltage drop

5. light flashes at low RPMs - bad slip rings

6. light glows dimly at all RPMs - open diode/diodes

Loren

How about this? Light works when key is "on" not running. Light doesn't come up when driving, but battery is not charging up?

8 year old battery died last month. I replaced it but didn't drive it much until now. I find that the car isn't charging up.

my related thread. http://forums.pelicanparts.com/porsche-911-technical-forum/392155-alternator-battery-failure.html?highlight=alternator+light

"Light doesn't come up when driving, but battery is not charging up?"

1. Bad regulator
2. Voltage drop from alternator
3. Bad battery
4. Weak alternator

A voltmeter should help locate/solve the problem.

Another scenario I just experienced: light on bright whenever car is running. Cause was bad diodes. Alternator was charging over 15v at all times!

Is this a Porsche specialty shop or Sears Auto?

Anyone who calls himself a "mechanic" and doesn't know how to troubleshoot/test a voltage regulator shouldn't be working on your car. He wants to replace it without knowing it's bad or not? If that's not the problem, then what? You own a shiny new (un-needed) voltage regulator.

Find another mechanic.

Using the voltmeter I get ~11.9 V, sam as when I test just the battery. The battery is brand new but I have driven a couple of times on it without testing it for voltage so it's low now. How can I isolate between the alternator and the VR...or does it not matter since they are replaced together on an 83?