frying altenator's?

What could keep burning up altenators? My original went bad so I bought a "guaranteed" good used one. Put it on nothing had it tested it was now bad.
Bought a brand new one from Advance and put it on last night. Today tested while running and now its only putting out 11.76-11.82v and only 30A. What could cause it to go bad again. All fuses are good, batteries are good, all wires are tight. Also while running the charge light is on but if I shut it down and start up again occasionally the light is out and it kinda sounds like I have an air leak or something and the volts are at about 10. After a few minutes the sound goes away and the light comes back on and the volts jump up to around 12. Thanks in advance.

Advanced auto parts suck. I had the same problem. Got my money back, after the 3rd junk lifetime alt. Spent a little bit more at Napa. But got a good one the first time around.

My only off the bat idea that would potentially want to toast an alternator is if the glowplug relay is stuck on or similar. Bad alternators are a very common story on the superduty.

Gotti2k7 said:

Advanced auto parts suck. I had the same problem. Got my money back, after the 3rd junk lifetime alt. Spent a little bit more at Napa. But got a good one the first time around.

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Yeah I'm starting to get that feeling. I have it off and was going to run to O'reillys to have it tested.

Tom S said:

My only off the bat idea that would potentially want to toast an alternator is if the glowplug relay is stuck on or similar. Bad alternators are a very common story on the superduty.

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Where is the GPR? I thought driverside I was gonna check all wires/connections for continuity to see if theres a break anywhere.

In the valley.

it's the back one..
the front one is for the air intake heater..

Yeah I went back to advance and had it tested it was bad. They tried giving me the last good one on the shelf so I told them to test it. Low and behold fails for D.C. volts too. Got my money back went to O'reillys and am extremely happy with them. It tested good put it on and still had a problem but it was my fault. I figured it out with the test light. I messed up when I replaced my cables. I accidently put the fusible link and wire that runs to the gpr from the starter relay on the wrong post on the starter relay. Now its running like a champ. Thanks for all the input/advice.