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?
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.
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.
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