battery drain

[Dolfinz]

Well, I finally have the car running but now it appears I have an electrical issue.  When the battery has a full charge the car starts just fine but the alternator gauge has a slight negative reading.  After running for a bit and shutting it off, the car tries to start but since it has been running on the battery there's not enough spark.  I have a brand new alternator that clearly isn't charging the battery when the car is running.  Any suggestions as to what the problem could be?

[Zed Head]

Can't remember what car you have. and if it's been modified.  Things changed over the years.

[SteveJ]

It could be the voltage regulator. Also, make sure you charge the battery fully. Running the car with a battery that is too weak/low can damage the alternator. Do you know how to use a voltmeter? You may also need to use an ammeter. This type can be helpful if you learn how to use it. https://www.amazon.com/Current-Auto-Ranging-Digital-Ammeter-V-Alert/dp/B094R8CB4W Until you can take some measurements and diagnose, you're just throwing parts at the problem. While you may be able to solve it that way, it tends to be more expensive.

Also, following what @Zed Headsaid, go to Account Settings (Click on the dropdown at your username if you're using a computer to access this site.) and then go to Signature. Put your car information in the signature. That will help people know what car you are working on. There are wiring differences between the years.

 

[Zed Head]

I found an old thread.  Pretty much original owner.  So, external regulator, old alternator.  The VR's go bad eventually, but usually go high voltage.  Might just be a bad alternator.  Could even be a bad connection on the back of the alternator.  Pull them off and clean them up and see if things are better.  You'll need a meter like SteveJ says.

This is a sign that there's no alternator current - 

1 hour ago, Dolfinz said:

alternator gauge has a slight negative reading. 

 

[Dolfinz]

It's a 1974 260z Nov 73 production I have now owned for 44 years. As I stated the alternator is new.  Prior to rebuilding the motor it had no electrical issues.  But, it sat outside for a year and it dealt with monsoons and heat during the rebuild process during that time.  I know how to use a voltmeter and ammeter as I am an Electronic Engineer.  I'm just looking for somewhere to start.  Ammeter from alternator terminal to RW wire to confirm current is a start but what could be bleeding the current from there?  Possibly the shunt?  Isn't that the feed for the alternator gauge?  Why cant I just take the output from the shunt directly to the battery and bypass any potential bleeds?  I'm going to rewire the front harness myself and eliminate unnecessary wiring and get down to what's actually needed.  Is this a possibility?

[SteveJ]

1. Load test the battery to make sure it is good.
2. Make sure the battery is fully charged.
3. Download the FSM if you don't already have a copy. Focus on the EE section.
4. Use an ammeter (not the gauge) to look for any drains on the battery. Hint: unplug the voltage regulator to see if that kills a drain.
5. Test the charging system components, using the FSM as a guide.
6. Make sure you are making notes on what & how you test with the readings/results so you can share with us along with details of what you have worked on/modified.

If you're not sure of how the charging system works, then I would advise against modifying the wiring. Especially with the 260Z, if you don't know what you're doing, you'll quickly wind up with a car that does not start.

[Patcon]

New alternators aren't always good

[siteunseen]

I learned to have them checked right out of the box, before I leave the store. Burn me once, shame on you. Burn me twice, shame on me. 

[Roberts280Z]

One of the handiest tools I have is a clamp-on DC ammeter.  Not only can you check the charging current, but on a low range you can check for those things that drain your battery in a few days.

[mailnome]

Those amp clamps are handy. I’ve got one with BlueTooth

I bought it when I went through swapping out 4 remanned alternators into my 4Runner. Yes the quality of remanufactured parts now is chit.


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[Dolfinz]

Can anyone tell me what the normal current draw for the battery should be?  I have studied the wiring diagram and the white/red wire from the alternator goes to the shunt and through the fusible link to the fuse block.  The white wire from the battery goes to the shunt and then also through the fusible link to the fuse block.  I will pull all the fuses and try starting it again and see if the battery charges but if it doesn't I can only assume there must be a partial short to ground in the harness somewhere.  Does this make sense?

[Roberts280Z]

If you're talking about the draw with key out, and lights off, that could be anywhere from 0 to 25 ma, depending on car alarms or any other remote gear.

I paid $35 for my clamp-on meter from Amazon.  That particular unit isn't available, but they currently have a unit for $48.  Just be sure you get one that is good for DC current measurements; the cheaper ones are for AC only.