1982 Vette charging problems

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- 82vette
  
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posted
18 years ago

Sun, Jan 8, 2006 10:25 PM

Help please,

Background...(1982 Vette) driving home the other evening and lights started getting dim, barely made it home. Charged battery and tested Alt. Not charging. Battery took charge. Removed Alt and took to Autozone, tested fine. It seems I have done something that is not allowing the alternator to charge correctly. Just prior to this I started replacing gauges with aftermarket types, I did short a piece of the gauge backing/strip. Possible the problem but plan on eliminating the backing. Other things to consider, power at back of alt to battery (screw), Two wire plug - Power at red wire, no power on brown (believe this the problem). Not quite sure what or where the brown wire goes. Anyone out there have a suggestion?

Bob

snipped-for-privacy@cox.net

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- PJ
  
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posted
18 years ago

Mon, Jan 9, 2006 2:51 AM

Hi Bob,

Sounds like you are on the right track.

Don't have the wiring diagrams for the '82 but on the '79 thru '81, that wire goes to the GEN warning light. The other side of the GEN light goes to the return for the gauges. From there, the instrument panel and cluster returns get involved with other indicator lamps, the choke relay and the tach. Best to get an '82 diagram to work from since there's some solid state stuff involved.

Inside the alternator, the terminal from the brown wire connects to a pair of transistors in the regulator circuit. I don't have enough detail to tell what that circuit does but I suspect that the changes in gauge wiring have disturbed the ground resistance in the GEN light circuit and may be shutting down your alternator.

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- Tom in Missouri
  
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posted
18 years ago

Mon, Jan 9, 2006 5:27 PM

Aftermarket ammeters (amp gauge) are often real ammeters and measure actual current. Factory amp gauges measure a voltage drop across a known resistance and do not have actual current through them. So you could have blown something with a real amp gauge.

The alternator for an '82 is an internal regulator (1969-up) and is easily damaged, often by transient spikes such as during jumping another car, loose battery connections (arcing a cable to a terminal), and so on.

What frequently happens is that you lose one phase on the alternator. This will test find on the crude analog testers in the typical parts store. It will usually only show slightly under a heavy load. But what happen is if you imagine three sine waves 60 degrees apart so that you have evenly spaced peaks. On full wave rectified, you have three peaks, then the lower half is flipped on top by the rectification and you have peaks 4,5, and 6. This brings you back to the beginning of the cycle.

Now if you lose a phase or if one phase rectification goes out, you will either have peak, peak, zero, peak, peak, zero on voltage or you will have peak, peak, peak, peak peak, negative peak. Either of these will allow a cheap tester to show a full 12 - 14 volts but the actual voltage and current is severely diminished.

Return your gauges and wiring back to original, replace the alternator.