Nissan Repair: electrical problem, nissan 240sx, side fender

Question
Hi Von,

I have a problem with my 1989 Nissan 240SX(5 spd). I took it to several mechanics(were not Nissan dealership, too expensive) and they couldn't find what causes this problem.

Here is the description:

I put a new alternator, starter(including starter relay: the blue thing that attached on the passanger side fender, right next to the battery), and battery within a month. However, when the battery is fully charged, it runs and everything seems fine but after awhile driving around, the bettery indicate light turns on with the brake light and the dash-board starts making some noise(it doesn't happen when battery light is turned off). And sometimes when I park the car, the battery is completely dead and the car doesn't start. I just took it to a my friend(a mechanic) and we did battery test, alternator test, and starter(also the relay) but they work perfectly normal.

It seems like bettery is not getting charged from alternator while driving(the battery was charging when the gear is at neutral).

My car doesn't have any high-output stereo or anything that really takes much power that much so I have absolutely no idea what is really wrong with the car.

That is my daily driving car and the only one I have and I'm renting a car right now. I'm in a desperate need of someone who is expert on old Nissan car like mine.

I sincerely look forward to hear from you soon,

Ray

Answer
Ray,

The output of the alternator should be tested at both the alternator and the battery.  There is a hotwire that is switched, coming from the ignition key circuit that energizes the fields in the alternator and that is how they function.  If the ignition circuit or a relay is defective that could cause the problem.  There is always the option of wiring around the problem with another switched ignition wire to the alternator.