My 82 Brat has been acting up in the cold weather.  The voltage needle will read correctly sometimes and everything is fine as far as power output.  Sometimes, however, when I start the car, the needle is at about 9v once running, and it obviously isn't charging.  It drops off the scale when I turn on the lights, the car must  be running soley off the battery, because the lights are very dim and the wipers swipe really slow.  If I drive it around enough, the needle will pop back up and the lights will brighten.  I think it has to do with engine temperature perhaps, because turning it off and restarting does not make it work correctly, but it seems like the low battery light will blink on, then it starts to charge.  I don't know if that is a symptom or a cause, perhaps the light coming on "kicks" something on, or perhaps the light just comes on once the connection finally gets enough continuity.   I did notice some corrosion on my battery terminals, so that is where I'm going to start, I'll probably replace the batter (it's pretty old) and clean up the contacts to start.  I had the alternator tested when it was working correctly and it tested fine, so I don't think I need to change it out.  Any other suggestions on this issue?

Sounds like you have warn out brushes.

 

Sam

Check the Fusible Links-Next to the battery under a small Rectangle cover-To check them look to see if the covering is burned at the ends then pull on GENTLY to see if they come apart....The other thing to check is the big power wire to the ALT. and see if it looks burned or melted-it"s common on the old 1s and check the batt. cables under the rubber coating-they carrode inside-they look good outside but be gone inside Good luck

Check all your connections first battery, fusible links, and alternator wiring.

I think your model has external voltage regulator so that might be the problem if the alternator isn't. If cleaning all the connections in the charging circuit doesn't help clear the trouble then the regulator may be the trouble but I don't think the alternator is exempt as the trouble yet either.

'82 should have the internal regulator.

 

I have had issue with the positive feed wire to the fusable link box on a few of the BRATs I've owned. Mostly it was corrosion, but did have loose fitting connection at the box also.

 

As others have said, check all of the connections for the alt, battery cables, engine and body grounds.