AUTO MECHANIC PROBLEMS (AGAIN)

[My 2 cents]

I'm going to go a little further out on the alternator limb and say that it's unlikely that the wrong one was installed. For this to happen, all of the bolts, pins, the belt, the swivel shaft, electrical connections, brackets and perhaps other things would have to match up perfectly. In today's world of highly specialized design, as illustrated in previous posts, the chances of a "wrong" unit matching up perfectly are pretty remote, making the physical installation impossible.

I think your first mechanic was telling the truth and that there is another issue with the car. Why he couldn't find it is a whole other discussion.