Alternator tested fine but still not charging?
 

Hi-
I've read some threads with similar topics, but wanted to see if anyone could chime in. I've been chasing charging issues for a while, here's the scenario:

'78 911SC
Car stalled on me after tach needle bounced around and engine lost power, battery was dead.

1. Replaced 9 year old battery.
2. Cleaned every ground I could find.
3. Pulled Alternator (internal regulator) and had bench tested...was told it was fine.
4. Reinstalled Alt with new Alt belt and correct shims for belt tension.

Fully charged battery reads 12.63V. When I start the car and rev past 2,500 rpm's, the voltmeter never gets above 12.5V and actually doesn't change with rpm's at all. When I shut the car off, voltage jumps back to its normal 12.63V.
My question, can a bench tested alternator that seems fine actually be bad? Am I missing anything? What's next?
Thanks!
Brian

Does the idiot light in your guage work?
In other words does the alt. light light up when you switch on the ignition and go out when the engine starts.

Brian,

During bench testing, did the alternator put out 13.5-14.5 volts under load?

Gerry

I will double check the idiot light, but I'm almost certain it's performing as it should. When I initially started having trouble (tach bouncing, loss of power) the alt/gen light illuminated so I knew what the general problem was....

When I took the alternator to the shop, he just took it out back and tested it, then came back and told me it was fine... I don't actually know what it was putting out. Is there a way to test it in the car? I'm assuming you'd have to get to the back of it and obviously it's buried in there...

the idiot light has to work for it to charge.

did you check the ground from the tranny to the body? some forget about it or do not know it is there.

what about the ground from the alt to the engine?

car wiring?

Check charging light and see if it has a resistor in parallel with bulb part# 911 641 981 00 (91 ohms, 5 watts) does light go out after start if not exciter current is to weak because of 2 watt bulb you need 2 (111 971 511 ) piggyback connectors 82 and later models have a 4 watt bulb but cannot be installed in earlier models because socket is to big. Also is ther a ground wire between engine case and altenator? There is a bulletin on this problem. Regards tom e-mail me for pics. tjl502man@aol.com

OK, will double check the alt light in the dash.
Yes, definitely did the tranny ground strap and the alt to engine ground very well...

I had a very similar problem to yours. Alternator checked out fine on a bench, battery good, replaced/checked several grounds, etc., but it wouldn't charge in the car. Keep digging. My problem turned out to be a connected but not (very) tight wire at the starter. I tightened that wire and problem solved. I got very quick at pulling an alternator...

Interesting, thanks guys.
I'll check the starter connections too.

Hi-
Just wanted to give you all a quick update on my alternator/ charging issue. After determining that my idiot light was functioning as expected and all grounds were done properly, I zeroed in on the starter. Sure enough, the spade from the alt had finally split in half after 32 years. I went to my local starter shop, got the right parts and a heavy duty crimper and fixed the problem. Thanks KNS, you were right on!

Great news! Glad you found it.

This is one I will log into my memory bank. This board is golden!

I'm chasing a charging gremlin right now as well. I'll be sure to check my starter tonight for any wiring issues!