Where is the alternator on a 1990 300zx located?

It appears the alternator is low on the front of the engine on the passenger side. This link is how one guy replaced his. Truthfully, if you're asking where the alternator is, you probably shouldn't be attempting to do anything with it. I strongly suggest you search for the factory service manual for the correct year and buy it. They usually have reasonably good step by step instructions, and are invaluable for repairing your car.

Good luck!

http://300zx.tombeauchamp.com/04_11_01_maxima_alternator.shtml

Jeff