Hmmm, 2 different AutoZone shops said the alternator was bad and your mechanic said it was a huge short, but the alternator was okay. Obviously AutoZone stays in business selling parts, your mechanic stays in business repairing cars. Did the mechanic test the alternator the same way the AutoZone guys did?

Estimating $200.00 to repair a "huge short" seems a bit suspect to me as shorts can be a real pain to track down and take quite a bit of time. You mentioned the local dealership wanted $99.00 to test the battery and Alternator, and that was almost half the Alternator replacement cost. I wonder what kind of Alternator your mechanic installed for around $200, as a Bosch or Denso rebuilt from FastLane is about $200.00 on its own.

My guess is that Autozone may be correct, and your mechanic may be trying to dodge a warranty job by charging you $200 to replace a shorted Alternator. Since your battery lamp went out, though I doubt the problem fixed itself, you may want to at least look at your voltage regulator for irregular brush wear.

Do you have a voltmeter?

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1993 190E 2.6 135k
1989 Ford Thunderbird SC 5 Spd 79K