Nissan Repair: 92 Maxima SE starting problem, neutral safety switch, battery cables

Question
my 92 maxima SE has been giving me some problems. recently, i was driving to work and it would die on me while sitting at the red light. but it would start back up and it would die again at the next red light and start back up again. i changed the fuel filter and put some fuel system cleaner in the tank. the engine runs fine when it's running. then the next morning it wouldn't start at all. i thought it was the battery so i replaced it and it started right away. drove it around for 30 minutes and it didn't die on me. later that day, it wouldn't start again. but it would start only if i jump-start it. drove it around and it was fine. the next day  i couldn't get it to start again even if i jump-started it. i got impatient i didn't bother trying to start it for a couple of days. then i thought it might have been a faulty  neutral safety switch that prevents it from starting. so i played around by shifting the gear up and down and back up  to PARK and jump-started it and it started. as soon as i got it going i drove it to the dealer to have it diagnosed. the check-engine light never came on during this whole ordeal.  the tech at the dealer told me that i need a new alternator. i was expecting that he'll tell me that i need a new neutral safety switch -and maybe a new battery- instead of the alternator. i'm not sold on their diagnosis and didn't have the alternator replaced. i'm picking up the car today and i hope you can help me decide which way to go with the repair. are they correct on their diagnosis or is it something else? i don't want to spend $400 and the car craps out again in a  week. so please help. thanks in advance.  

Answer
Hi again Alan,

Did you do the test I recommended? Was it not the alternator?


Hi Alan,

Yes, it is a bad alternator. Have it replaced and you will be fine.

One way to verify that it is the alternator, have someone jump start you and then disconnect one of the battery cables. If it dies, then you need an alternator. Do this with your lights, a/c and radio on. This puts a load on the alternator. Sometimes an alternator will have an output of like just over 12 volts at idle with no load, but with a load it will have only 9 or 10 volts. This is why the check engine light did not come on. It sees that the alternator has output, but the output is not enough to charge the battery under load. When you jump it it charges the battery slightly and your car is running on that charge.