So I just recently acquired a 86 NA 300zx. I am having a problem where my battery keeps draining after my car turns off. I was told the battery is good after it was tested at AutoZone but it is on the old side. For now I just disconnect the battery every time I shut the car off. Just wondering if anyone has had a similar problem. My battery terminals do need to be replaced but I dont think that would cause the problem.

 

I had the same problem a few weeks ago. Do you hear a click sound from the engine bay at all? If so, disconnect the fusible link on closest to the battery. I believe its ignition and fuel. If the battery still dies, get a ammeter and look it up in series with the battery using the negative battery terminal and check the amp draw. After that, start pulling fuses til the amp draw goes down. Once you have found the fuse work from there.

 

Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen. go to a real battery shop not autozone, oreilly or walmart