Nissan Repair: 96 MAXIMA, defective alternator, auto parts store

Question
QUESTION: I replaced the alternator on my 96 Maxima two weeks ago is there any reason (other than a bad alternator)that the car will run fine as long as there is nothing on(heater,headlights,etc.)Once you turn anything on the alternator wont put out enough to recharge the battery. im at my wits end with this car any help you can give me will be appreciated.  thanks so much

ANSWER: Hi Lisa -

Need some clarification.
Are you saying that when you use the accessories, once the car is turned off, it cannot be started, and has to be jumped? Otherwise if nothing is used, it starts OK?
Has the alternator been tested for output?
Has the battery been load tested?

Let me know -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: yes if i us accessories once the car is shut off it has to be jumped. The battery tested fine and the alternator tested fine as long as no accessories were running.I cant drive the car at night because the headlights alone will drain it.The gentelman at the auto parts store said the car will run just fine as long as i have nothing on.When he tested it without anything on the alternator was at 13.5 once i turned on radio,lights,fan it went to 10.5.

Answer
Hi Lisa -

Your comment "alternator tested fine as long as no accessories were running" is the key. There is a field test for an alternator that you put a volt meter on it and run it without load, and a load test where you place some electric load on it at the same RPM. Both have to read 14V. If the alternator runs under load and not reading 14V, then it is a defective alternator.

Hope this helps -
aloha
calvin