2001 Kia Optima Bad alternator? Advice pleasae.

I have replaced the alternator 3 times in my car. I know when my alternator is bad, but the other day I replacewd my power steering line, and arched the hot alternator wire. Well my fuse blew so I replaced that, then my batteryu died, I got a new battery put It in this morn, took my car to adavnced and had them do a alternator test. I thought when they preform that test with their machine the one clamp is supposed to be aound the postive battery wire, well the lady put it around the neg. So the test was done and it says my alt was charging at 12.1 volts, but all the times alt has went my battery light on my dash has came on, well the light isn't on and I just replaced my alt about 4 months ago? I mean its going to read 12 volts because that is what the battery puts out, if that clamp was on the neg, So I think the lady did the test wrong, if anyone has any idea please let me know, before I replace my alt for the 5th time! Thanks