1 Answer

First off you need to loosen the tension bracket from the top, it's a longer bolt slightly above the alternator, now you need to get under the vehicle, there are only really two bolts holding it on, one very long one and a shorter one. After those are removed you can unplug the alternator from its power source on top...now to remove it..a little tricky! You now have to remove the A/C motor which prevents you from pulling the alternator out from the bottom..it is held on with 4 bolts..once it is off you can drop the alternator..
I don't actually follow the second part of the above answer because removing an an a/c motor is not quite easy. I removed the alternator from the top by removing the big radiator hose and its housing unit from the engine. When you put the housing back, just make sure you seal it good so water won't leak. http://wiki.answers.com/Q/How_do_you_replace_the_alternator_on_a_1991_Infiniti_G20