Hmm I had mine rebuilt 3 years ago by a local place that has a good reputation and I've used before since the early 90's. I was kinda disappointed when the alt died after only 3 years and about 20k miles, but it looks like it did good by others experiences on here. And it turns out it was probably the battery that took it out as it totally died about 3 weeks after replacing the alt!

To the OP, my battery tested good when the alt died, but try a new battery if you can get your hands on one to test with.

 

Check out all the wires connecting to the alternator. Trace there paths and be sure there are no shorts. Sounds like a short to me. Possibly grounding where it should not. On my old 97D1 I found that my positive battery wire was grounding to the frame. This not only fried the alternator and battery but caused a serious short in the transmission side of the harness. Sometimes mechanics are violent when performing repairs, maybe wires were damaged or left to rub through on the frame. Check you frame for any positive voltage. This of course will let you know you have a short.