Test an Alternator ?

[Tori]

Feel like i'm talking to myself here, but what the heck...... Found (hopefully) the culprit. Got the Alt. the rest of the way out and discovered it could be drug back out of the shroud a few more inches allowing access to the wiring/terminals.
Anyway,.... I had left the positive (large red wire terminal loose @ B+ The nut was there, and run about 1/2 way down, but not tight. I can see that creating an intermittent charge issue, but the two red wires were making contact with the post and the nut. Or... maybe the poor contact created some voltage spikes and fried something internal to the Alt ? Maybe there's a fuse somewhere that could have blown ?

Thoughts on this ? Anything i can test with this in my lap ? Should i try reinstalling and see what happens, or just replace the Alt. ?

[Tori]

Fixed.

[Craig]

Ah, what a good feeling, eh? Was it just the loose nut on B+ wire?

[Tori]

That was the only thing i changed. Definitely a good feeling. Gonna run her and my gal down to Santa Barbara for the weekend now.....

Cheers !

[ItzaMe]

Originally Posted by Cooper911SC

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,
e.g. @ alt. B+ post, @ starter connection, or @ battery connection

5. light flashes at low RPMs - bad slip rings

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

Thanks to Loren at Systems Consulting!

If you’re only seeing 10.5V it’s not charging... time for a rebuild or replacement swap in.

Cooper

Bringing this thread back to life.

Good break down post above. I just got an 82 911SC delivered last night and the generator light flashes on and off as I drive the car. I know these alternators are known to be some of the worst in this year car.

I will be digging into it more today. Need to figure out what voltage reading I’m looking for when testing. Hoping it’s a simple fix so I can get the car on the road!