Alternator not charging - light dosen't come on?

[bobswei]

I recently notice that when I turn on the ignition on in my 72 T, the alt light doesn't light up. Then I realized my battery wasn't holding a charge. I checked voltage at the battery with engine idling around 12.5 volts. I was expecting 13+.
Doing a search, I found this comment from another thread: "...have you confirmed that the bulb for your alternator light is good? It needs to work to "excite" the regulator, thus resulting in the alternator putting out a charge"
Anyone know if this is a valid reason for my situation?
Thanks...

[wwest]

The current flowing through the bulb (and sometimes a parallel resistor) is used to energize, initially, the rotor windings via the slip ring brushes. Slip ring brushes are a VERY common failure for high mileage vehicles.

[timmy2]

Pull the oil gauge and check the bulb. If it is burnt out the car will not charge....
About a $2 fix...

[James Brown]

need voltage to make voltage on a alternator. check the battery voltage prior to starting, then after. Kinda wish we kept the generator, less hassle.
I removed the oil qty gage and replaced it with a volt meter from palo alto speedometer.

[bobswei]

OK, I think you may have gotten it. I checked the bulb on the battery and it didn't light. I had a few spares and tested and they lite up. Unfortunatly, I already had the alt out of the car so I'm cleaning up the fan before reinstalling. I'll post as soon as it goes together. But I'm feeling good about this....
Thanks for the responses.

[wwest]

Were I you I would pop the alternator open and have a looksee at the wiring insolation/insolator condition.

'78 911...~100K.....NOT pretty.

[bobswei]

OK!! All the wires lookd good, from what I could see on the alt. Clean fan and back together and it's throwing out 14.6 volts at idle. And a new bulb lights up. Yea!!
Thanks for all the input.
Bob