I just installed a new alternator and battery. However the battery will go below 12.6V overnight which won’t allow the car to turn over/start. I have done a lot of diagnosis with a multi-meter and one with an Amp Clamp. No amps seem to be drawn and only one fuse is drawing power. The fuse #36 is drawing 1.2mV and once the fuse is removed, the items it is mapped to do not respond as expected. Fuse #36 is suppose to control the Emergency Flashers, instrument panel and the A/C Control. But when the fuse is pulled the turn signals and instrument panel go dead BUT the flashers and the A/C controls still work. Disconnecting the turn signal wiring harness made no change in the readings. The only other thing I have noticed is if I leave the driver’s door open long enough for the inside lights to turn off (the radio too), fuse #36 reading goes to zero. And once the door is shut and reopened, the 1.2mV draw returns. I disconnect the door striker and checked it, but nothing changed. I should mention that this problem started after the (professional) installation of the correct alternator. A check of both the battery and alternator show no signs either is malfunctioning. Where or what do I do next?
I am wondering if the battery goes dead with the fuses/components unplugged?
And a 12.4 volt battery should turn the starter over without issue. I am thinking more along the lines of a faulty/failing starter and or poor cable/connections to and from battery. This includes at the battery, grounds and alternator connections. Along with possible corrosion in the battery cables themselves. After all it going on 20 years old.
If the fuse is removed, the battery is still drained below 12v. The cables to the battery are clean and in very good shape. Have any other questions, or better yet some suggestions on what to do? That’s what I was hoping to get from this site.
I would perform another test since you are committed to worrying about the battery and not so much about having it start when you want. Though I still think it is what I said.
BATTERY: Fully charge the battery – Disconnect the terminals from the car and leave it set 1 – 2 days and recheck the battery. I HAVE myself tested many NEW batteries with a battery load tester and they test good, but were in fact BAD. They would not hold a charge and would act just like yours. An option would be to put a KNOWN good battery from another vehicle in it and see how it does.
STARTER: (assuming you have a good ground at the starter case)When the engine will not start/turn over: Have someone hold the ignition key in the “START” position while you check for battery positive voltage at the “S” terminal on the starter. If you see battery voltage and the starter is not turning the engine over, you guessed it. Replace Starter. If you do not see battery voltage at the “S” terminal then you will need to back trace for the disruption.
PARASITIC DRAW: Still convinced it is something drawing voltage in the vehicle. Check for a parasitic draw. https://www.wikihow.com/Find-a-Parasitic-Battery-Drain#