scorciae

if i have the headlights on, the rear defroster and hit both power window buttons, my batterty light comes on and my car almost shuts off, do i have a bad alternator, or is this a common old vette thing

lars

A couple of possibilities:
1. If the alternator is the original, stock unit, it will be sized to support the loads you're referring to. Often, the alternators have been replaced with rebuilt units from Checker, and do not have the correct amp rating. The result is what you're observing.
2. If your brushes are worn or your internal regulator is not up to snuff, you can end up with less than spec amp output from the alternator. The units are very simple to rebuild and diagnose. If you'd like a copy of my alternator rebuild paper, drop me an e-mail request to:
V8FastCars@msn.com

GaryS

Although that is a bit of a load on an old alternator, I don't believe that your car should stumble like that. As Lars said, you might have an alternator problem. Try pulling your alternator out and taking it to Pep Boys, Advance Auto, etc for a free test. BTW, rebuilding one of these alternators, to include voltage regulator and bearings isn't that tough. Beyond that, consider having an alternator/starter shop rebuild it.
Gary

BSeery

My 1980 stock alternator had the same problem. It is not a 10-SI alternator, but something like a 15-SI.

I converted mine to 100 AMP output and my problems went away.
If I had to do it again, I would get a 100 - 140 AMP chrome one from Summit to dress up the compartment. Plust the Summit alternators are a 10-SI, so they are smaller in size and parts are A LOT more common.

DaveL82

There is a connector just above the passenger side valve cover and to the left (looking from front of car). This connector supports all the current (wires from the starter battery terminal) for all accessories and HEI ignition. I found on my 80 that one of the pins had over heated and had corrosion.

This pin also supplies current to the HEI ignition, which needs full voltage to work properly, so if the voltage drops the ignition can begin to miss fire or not produce enough spark to fire the mixture. As a temporary fix, I pull the wires from the connector, crimped with heavy duty terminals, soldered them directly and then covered the connecttion with heat shrink tubing.

After the fix, the car now maintains the correct voltage (never did that since I bought the car 17 years ago) with the defroster or AC on.

May not be your problem, but I would check it out. The connections for the main power wires are critical. I now they used the connector to ease assembly at the factory, but the connector is not a good design to handle the current of later cars with a lot of accessories.

Dave