With engine off, battery hooked up, and alternator lead disconnected, I get 13.08V from lead to ground. With engine running, alternator lead still disconnected, and going from alternator stud to ground I get 0.3V to 0.4V. Also get in range of .2 amps.

 

New development - after pursuing several of your questions, and getting the above listed results from the alternator, I pulled the alternator and took it to AutoZone again for testing. This time, they have a new machine where they actually "install" the alternator and run it - it failed immediately. Bought a new alternator and installed it. Amp gauge is now showing positive - %#@%$@#%$# only took several years!!!!!!

But, a problem remains. At idle the gauge shows positive charge(Yeah!) but the Gen light is flickering and because I have the door open the courtesy lights are on and they are flickering. When I rev the engine that all goes away. Gen light goes off completely and courtesy lights run steady. Something still not right.

So here's a REALLY stupid question: when you mentioned above making sure the alternator has good ground, I assumed you meant through it's mounting brackets(which I did strip and paint a few years ago as part of a complete restoration of the engine compartment), but while removing and install alternators today I noticed there is a ground stud on the back of the alternator. There has never been a ground wire for the alternator in this car since I bought it and the Gen light has always flickered at idle. Has it been missing a ground wire all this time, or do the mounting brackets cover that?

 

I tried running a dedicated ground wire from the ground stud on the alternator to chassis. Made no difference. At a slightly higher idle - maybe 900 to 1,000rpms, Gen light goes off and no flickering. If I kick it down to lowest idle - 700 to 750rpms, Gen light comes on and amp gauge even goes negative on me. If I goose it, light goes off and amp gauge goes positive. Big improvement over what I started with, but something's still not right.

 

Good deal. Your second to last post (voltage test) told me the alternator was bad!
Your original wiring harness would have had a separate ground wire that bolts to the back of the alternator case. You can see if you can find it, someone may have snipped it off, or run a separate ground wire. Also make sure your voltage regulator is well grounded. The flickering lights might be from having a jittery or marginal operating regulator, the original style is mechanical that has breaker points. You can get an electronic voltage regulator that is more reliable and steady.

 

Any ideas on why the Gen light is on at low RPM?

 

With engine running, check to see what the voltage reading is, both at the alternator and at the battery.

 

With new alternator, engine running and kicked down to low idle with Gen light on, get 12.8V at battery, 12.7V at alternator and 12.6V at regulator. With it running just slightly higher idle, those 12s all become 14 and the Gen light goes off.

 

That's too low at idle. If it were my car, I'd replace your voltage regulator with an electronic one, if you haven't already.
If it were my car and I didn't care about "originality", I'd convert it over to an internal regulator style alternator.
One more thing you can try, run a jumper wire from the battery to the at the regulator. You may have bad wiring not carrying current to the exciter wire there. If you look at the earlier diagram, that would go to terminal 3 on the regulator. Also look at the junction block in front of the battery. Make sure all those wire connections are good, that's a critical spot.

 

Thanks. Ive spent thousands to keep this original. I like the idea of the jumper. I'll try it this weekend. Traveling now.

 

I figured you were going to say something like that. If all your wiring checks out ok, which I have a feeling it might, then the next step would be to adjust the voltage output of the regulator (yes, the breaker style is adjustable). The adjusting screw is inside the regulator, at the base, opposite side of the four terminals. Instead of rewriting the procedure, I can make a copy from my service manual. For kicks, I'll see if there's a good one shown online.