Nissan Repair: 1990 300zx electrical problem, selenoid, electrical problem

Question
hey i have asked several questions pertaining to my car and your answers have been really helpful, so thanks. but now i am having another problem... my ground was bad on my car and the power wire was also bad... i checked the selenoid on the starter and it was bad as well. i replaced all of them and checked the computer to see if it was still working. after that i got a new battery and the car started fine and i drove it around some. i parked it and the next morning the battery was completely drained. i did not leave anything on so i couldnt figure out what had happened. i jumped the car and it started but would only run for a little while before it lost battery power and died. i checked the belt on the alternator and it was a little loose so i tightened it up. i recharged the battery and started it up again and let it run for a while to see if it would die. i checked the voltage on the battery before i started the car and it read 12.5 volts. i turned off the car and the voltage still read 12.5 volts so i assumed that the alternator was working and the problem had just been the loose belt. the next morning i went out and the car would not start again and the battery read 2 volts. somehow it had drained overnight. i dont know how. nothing had been left on, no lights nothing... i would really appreciate some advice. it seems that when the car is left for extended periods of time, as in 6-12 hours, it somehow drains the battery... thanks, josh

Answer
Josh,

The alternator is supposed to put out 14.2 volts.  The 12 volts runs the car and the rest charges the battery when it is running.  Make sure the wires to the alternator are hooked up correctly.  But, for me I would think the alternator is gone and that is what is draining the battery.  There are diodes in the alternator that, when they blow, will allow electricity to flow both ways.  When the car is off the battery drains to ground through the alternator.  And, if the wiring is correct, we know the alternator is blown since it is not charging the system.  Replace the alternator if the wiring you replaced checks good.